How can I remove polyurethane while it is still wet?
Okay first: don't use PolyShades for anything...ever. Its the worst.
Second: Stripper is great except when its not. Sometimes certain strippers react to certain finishes in a way that is...undesirable. Then you have a mess. I've been doing this longer than I care to remember and I still have weird results now and again. No rhyme or reason. CitriStip gel is pretty good, and safer to use than the solvent based variety.

I like to remove finish with a scraper, especially when green. It cuts through the finish quickly and doesn't clog like sand paper. Its a modest investment and learning to sharpen them properly takes a few tricks (see William Ng's tutorial on Youtube) and profiled moldings present a bit of a challenge, but its a skill worth learning if your into working wood. 
Good luck.