So I went into a bike shop today and swapped my cassette and chain from 10 spd to 9 with bigger gears for hills. Definitely an improvement over the 11-32 cogset I was running before.

I want to replace my small and middle chainrings too but they are Sugino and I couldn't understand the xplanation as to why but the gist of it was that they were only willing to swap out the entire crankset. That doesn't seem reasonable to me at all but this is the second time in my life I've had a shop refuse to swap chainrings. I think the first time was in France and I don't recall why they said it couldn't be done either. But yeah, I'd really like to avoid buying a whole new crankset just to get more mountain appropriate chainrings...

So two questions:

Is the swap easy to do myself and can it be done without purchasing a bunch of specialized tools (I am nomadic) and can I put chainrings from other brands onto Sugino cranks?

I would have thought all that matters is getting the desired number of teeth and appropriately placed bolt holes.

You went from 10 to 9? Odd choice but ok.

Depending on BCD (bolt circle diameter) you should be able to swap chainrings though sometimes shifting might change as well? Some set ups might have issues shifting and some chainrings don't always play nice together but it generally is possible. However I will say sometimes it is cheaper to get a new crankset than buy all new chainrings.

It is easy enough to do on your own but you will need a chainring nut spanner for most stuff simply because a lot of crank manufacturers still cling to those old nuts instead of using hex bolts on both sides. However Wolf Tooth Components makes excellent crank bolts that are dual sided hex, made in the USA and come in some cool colors. I haven't fully installed them yet but tested them out on an old XT crank (with Biopacé chainrings for age reference) for the outer and middle cranks and they will work just fine (for double) the inner already uses a hex bolt and won't be seen.

If you are talking older style 5 arm cranksets, then Shimano and Sugino are slightly different. Sugino has what is termed a hidden 5th arm; basically the middle (on a triple) and large chainrings bolt to the "back" of the crankarm. Shimano has all 5 arms visible. Why does this matter? Well if you use a "Shimano" compatible large chainring on a Sugino crank, then the chain retention pin wont line up with the arm. I have heard, but not verified, that the centerline of the chainrings are different in relation to how they mate/bolt to the crankset, which may lead to uneven spacing if you mix and match chainrings. That being said, I did replace the 3 Suigino chainrings on a triple Suigino crankset with some TA Specialties rings, which use the "Shimano" standard. I did drill a small hole in the outer chainring and move the chain retention pin. Bike shifts just fine. I did not mix and match different chainrings though.

If you were asking the shop to recommend (and possibly do the actual replacement), I can understand how they wouldn't. Its incredibly easy to screw up the front shifting these days using parts that aren't designed to work together. Do they want/need an irate customer. Now if you had specified that you wanted xyz ring, then I would expect them to sell it, but you take the responsibility if it doesn't play well with what you have. Good luck.

Many years ago I swapped out my aluminum chainrings for steel ... 110; 50,40t, 74;24t,, they have proven to be very long wearing..

The only reason I can think of for a refusal to swap chainrings is that the rings are riveted in place.

A photo would help a lot. I am assuming this is a square taper five arm crank.

As long as the chainrings are bolted and not rivited to the crank arms, a five arm chainring should be easy to swap out.
https://www.sheldonbrown.com/cribsheet-bcd.html

Decades ago before chainrings started to include ramps and pins and such shifting aids, shifting was not quite as smooth. Thus you probably would end up with shifting that is less smooth, but that should not be a big deal.

In some rare cases, you might have to add a spacer washer under a chainring, but the best way to find out if you need one is to try the combination you want and see how it works. When needed it is likely if you mix 10 speed rings on an 8 or 9 speed chain. A thinner 10 speed ring can upset the spacing and require a spacer.

In the attached photo I put a generic (no name) 74mm BCD five arm 24 tooth inner chainring and a Stronglight 135mm BCD five arm 46 tooth outer chainring on my Campy crank with the stock Campy 42 tooth ring in the middle.

Eggman84 talked about a pin, you can see a small hole in the big ring in the six o'clock position, that is a small threaded hole so that I can use this chainring on any type of crank with the right bolt spacing.

Having done both I would say changing a ring is less problematic than changing an entire crank arm.

With the former you only have to worry that the rear derailer can pick up the extra slack from decreasing the chain radius (going from a large small ring to a smaller small ring). Your shifting position on the derailers won't change.

With the latter you have to hope the rings line up in the same position on the BB spindle or you wind up having to either change BB's or front derailer position. When I swapped crank sets from a Shimano to SRAM 42/32/22 I had to change BB's because the newly installed chainrings sat too close to the frame on the old one (I needed a longer spindle length).

+1 The lower end Sugino mtn cranksets have riveted chainrings. I run Sugino cranks on several bikes, the DX 500 mountain, and the DX 600 road. Both have easily replaced rings. Finding rings for the 4-arm DX 500 cranks is hard because the have been discontinued. I saw the hand writing on the wall a few years ago and purchase a couple of sets.

"Is the swap easy to do myself and can it be done without purchasing a bunch of specialized tools (I am nomadic) and can I put chainrings from other brands onto Sugino cranks?"

Changing chain rings is a bit complicated, special tools probably required, depending on the components. Other brand chainrings are often compatible with your crankset provided the BCD is same. Procedure to change chainring is typically as follows:

1. You need whatever tool required to remove crank from BB. Remove crank.
2. Next you need whatever tool to remove ring from crank. Remove ring(s).
3. Reverse step 2 - install new ring. Threadlocker is a very good idea for chainring fasteners.
4. Reverse step 1 - install crank.

Although you may be capable of accomplishing the chainring swap, you first need to know if your front and rear derailleurs are compatible with the chainrings. FDs are increasingly limited WRT size of chainrings and the jump between ring sizes. Shimano FDs typically have specifications for both of these parameters. RDs typically spec maximum cog size and overall chain capacity (how much chain the pulleys can tension). If the rings fall outside range of derailleurs' compatibility, you may have poor shifting, or worse.

You'll need to adjust chain length if you change chainrings. Proper chain length is determined by routing chain over largest cog and largest ring, and adding 1"/1 link (1 link = 1 inner half-link + 1 outer half-link, which many consider to be two links, not one - each half-link is 0.50").

Sugino cranks, particularly the touring-marketed XD 500, has a 74mm BCD and the smallest ring you can fit is 24t. This may be the reason the LBS tried to sell OP a new crankset - to provide capability to fit a smaller ring, for example 64mm BCD fits a 22t, 58mm BCD fits a 20t. Another possible reason, for years Sugino specified the XD series cranks as being Shimano 7 and 8 speed compatible, throughout the whole long run of 9 speed, even though they'd actually work pretty good with 9s.

It may be the LBS did not have confidence that a FrankenCrank would work with OP's FD, and chose the safer route of recommending a new Shimano crankset that they knew would work with Shimano derailleurs and cassette. There must be a million combinations of cranks/rings/chain (5-12 speed)/deraileurs/cassettes, and only a few work reliably, and few mechanics at an LBS will have knowledge, experience or ready access to good references to unambiguously determine acceptable component compatibilities. Why would anyone sell parts that may not work, dissatisfy the customer, result in returned parts you'll never be able to sell, all for what is likely $10 profit on rings. LBS makes 3X as much on a crankset, it's easier to install, they know it will work, and the customer won't return dissatisfied.