I'm trying to empty a beer can and refill it with a less inebreating
liquid. If I use water, I can reseal holes punched in the bottom with
tape. If I try to use a carbonated beverage, it leaks. Any suggestions?

If you can find a can of soda or another beverage which just fits inside
your beer can (many do), you can cut the top off the beer can and slip
the other unopened can inside. This has the advantage of allowing the
actor to pop the top on the "beer". The beer can top has to be cut off
BELOW the rolled rim, so that the cut edge will slide up under the rim
of the outer can. Be sure this edge is flat and as smooth as possible.
You'll still probably want to wrap a strip of clear tape around the
whole edge for actor safety.