I'm running a Specialized Roubaix Pro SL2 with a mix of Red and Force components. My chainrings are 50/34, my cassette is 11-28 (Ultegra I think). Living in Vermont I've been struggling with the Cat 4 and steeper climbs, I could really use one or two easier gears. I know, 34-28 isn't bad, but being a spinner, I just can't spin it fast enough, so I end up more like Jan Ulrich and have to pound the gears to get up our gap rides, resorting to switchbacking using the whole road at times. I was wondering if I can go to an 11-32 cassette and keep my Red rear and front Force derailiers, or can I go down to a 30 small chainring, (but then do I need to go down to a 48 big chainring)? I have the Pro model S-Works carbon crank (stock on this bike), so I don't even know if going down to smaller chainrings is an option which is why I thought the cassette option might be the better way to go..

may just have to add a the Long cage RD or at least Medium, if you will adopt a Triple crank.
Hollow tech stuff means whole crank as the tube spindles are attached tothe Rt Crankarm now..

Compact double .. 34:34 is the best you can Do..

I figure red can handle 54/39 rings and 11-28 cassettte, wonder if the Red RD can handle 50/34 and 12-30 cassette. Has anyone actually tried this? I know all the literature says 28 is max on the back, but I want to see if anyone actually tried the new 12-30 with the compact 50-34...

Wrap, chain take up, math is tooth counts (Big+ big ) --( Little + little ) .

don't own that exact kit . so Hands on owners of that combo,
May be a while before someone else pipes up.

good luck or just give it a try

You cannot go below the current 34T chainring by enough to matter as your crank's 110mm bolt circle diameter will accept a 33T chainring as an absolute minimum. If you really need a true granny chainring you will need a triple crank and SRAM does not offer one in any of their road groups.

The crux of the matter is getting the jockey pulley to clear the largest cassette cog. Frames with a longer derailleur hangers are more tolerant of "pushing" cogs beyond spec.

Try it and see. If it doesn't work, an Apex rear derailleur can be had for less than $80. And if you're concerned about mixing SRAM levels, don't be. Contador won the Giro using an Apex rear derailleur before WiFli became available for Red.

It's highly likely you'll need a longer chain.

This might help you.
https://home.earthlink.net/~mike.sherman/shift.html

I've used a SRAM Red WiFli (longer cage) RD successfully with an SRAM XG-1099 11-32 cassette in combination with a compact (50-34) crank set. Works beautifully and letts me keep my cadence > 75 on all but the very steepest grades around here. And I'm a poor climber... BTW, it did require an addition link length in the chain.

Generally good practice to change the chain when changing cassettes. Unless the chain is very new, I wouldn't personally add links.