Chain length: Non issue?
 

If going from combo #1 to combo #2, the chain length should change much as far as slack, correct?

combo #1
Shimano Acera M360 R-derailleur
FSA Dyna Drive 48/38/28
Shimano HG31 11-32, 8 speed
KMC Z7

combo #2
Shimano acera rd-410 R-derailleur
FSA Dyna Drive 48/38/28
Shimano CS-HG31 11-30, 8 Speed
KMC Z7

So, you're going with a cassette that has 2 extra teeth.

If your chain currently has 2 extra links slack when in the big/big combination, then you'll probably be ok. Otherwise, add 2 links.

Is the new cassette new?
How old is the chain? If you have more than 1000 miles or so on your chain, then throw it out too, and start with a new chain and a new cassette.

oops, I should have stated that combo #2 is going all new components, nothing physically reused from combo #1. Only reused if it matters are two associated part numbers which is the FSA and KMC.

Yes, the intention out of personal preference is to obtain a better slight "highway" gear at the time of predetermined, scheduled/yearly-winter-boredom-maintenance.
Nothing wrong with the old stuff, especially since the chain is semiannually replaced with a new one after a bi-monthly swap out with the pre-inspected/cleaned/lubricated and shelved last used chain.

I've come to like my method of maintenance as it really works well for myself. May not fit others criteria or check-off to there convenience factor list.

Hmm, as I read it the large cog on the new cassette has 2 fewer teeth, so totally a non-issue.

Just dont want to have chain slapping the frame rail.

Chainstay lenght? Same frame? or not?

How is going from-
11-13-15-18-21-24-28-32T
to
11-13-15-17-20-23-26-30T
Giving you better "highway gears", when the 3 smallest cogs are the same?

If you said I hate that 18-15 jump, I'd understand, since 17-15 is an easier "progression".

less shifting with the FD when using the 30T as well as a smaller benefit from not needing to shift right out of the gate regarding the creeper gear. Minimal benefits to some, considerably more rewarding on my end.

same bike, nothing else changed that'd impact the chain mech-x