I added 4 lbs of CH. My pH is 7.2 and I want to add some borax, which are at 30. The CH label says not to add pH plus the same day as the CH. Is that true? If it is, does it apply to borates too?

Yes, it applies. You don't want to add calcium and also raise the PH on the same day. It isn't such a big deal if you are well below the minimum CH level for a plaster pool (i.e. well below 250) and not planning to go above that right now, but gets to be rather important if CH is in the normal plaster range, and crucial when CH is above 400.

My CH is 125. I've never worried about it being low because I have a vinyl pool, but I was reading my SWG manual last night and it says the CH should be 200-400 so I decided to raise it.

Don't bother. CH above 100 in a vinyl liner pool serves no purpose except to enrich the chemical company. (And below 100 is fine in all but the most unusual situations.)

It you are bound and determined to raise CH, don't go over 200 on the same day as anything that raises PH.