HamNCheese writes:

From what I've read doing a search, there are actually
plaster mixes I can use to patch it that will set underwater, so I
won't have to drain it at all.

Imagine that. Let us know how well it works. Hard enough to work plaster
when conditions are ideal.

By the way, all portland cement products will set under water, including
ordinary pool plaster.

This is a pool that is in need of a
replastering in the next year or two anyway, so I'm not too concerned
with how it will look.

It's not just a matter of looks. A rough patch will just collect algae and
crud, and will be as bad or worse than no patch at all.