Eh... there's more he could do to the USCIS than cut pay, from what I recall of the few minutes I spent checking the relationship there. Pretty sure it's more or less directly subordinate to the stuff the presidency has full/substantial control over (vis a vis structure, functioning, etc.), so the scope of capability is... kinda' anything, roughly speaking. Least it looked like if he really wanted to, he could more or less fire any/every one in the USCIS, tell them all to stop working, freeze hiring (campaign promise), etc., etc., etc. Can't self fund if you're no longer allowed to do the stuff that funds yeh, heh. It'd be a procedural/legal hell to actually go through with, but the question is if that'd actually stop the folks involved.
Presumably there's some sort of limit(s) on what could happen there, based on whatever bit of legislature the USCIS has been being used by the executive branch to fulfill its obligations toward, but I can't recall there being a legal/procedural issue if the executive branch wants to just kinda' get rid of/gut one of its subordinate organizations by/while claiming intent to reorganize/restructure/etc. to (better) fulfill legislative responsibility (regardless as to if the intent to fulfill that responsibility is there, ha*). It probably hasn't happened much/at all, because deep sixing a major governmental organization without having transitioned its duties elsewhere/readied some kind of replacement/etc. is basically monumentally freaking stupid and by and large our previous executive branches has managed to at least have the cognitive stability to avoid something that colossal of a cock up, but...
*Structural inertia and whatnot being what it is, it's entirely possible for the process alone to take longer than a presidential term, which basically means if you had a particularly bad faith president, you could probably end up with them intentionally screwing around for their whole term and not really having to deal with consequences, because the results of their mess gets dumped on whoever comes after. Happens pretty often with lower levels of government, tbh. Governors or somethin' doing crap during their term(s) that have repercussions/don't really come into effect until afterwards, that the state/next governor/whatever ends up getting screwed by a few years down the road.