How difficult is it to replace a 1-handled shower/tub faucet with a 3-handled faucet? Do I have to make new holes in the tile? What about doing the same with a sink?

Hey Shelly,

"How difficult is it to replace a 1-handled shower/tub faucet with a 3-handled faucet? Do I have to make new holes in the tile?"
I don't know why you would want to but click on , http://www.plumbingsupply.com/escutch.html
And scroll to the bottom of the page and find three hole escutcheon plates, (see image). There are 6 to choose from both in chrome and polished brass.
However, This all depends on how large to opening the old valve left You may have tile replacement and holes to drill.

"What about doing the same with a sink?"
Kitchen or bathroom?
Regards, Tom