I have an applied patch in my Mercurial queue, how do I convert this patch into uncommited changes in my working copy (as though I'd never created the patch using qnew)?
Tell Mercurial to refresh the patch but exclude all files. This will leave all changes in the patch uncommitted in your working folder. You are left with an empty applied patch that can be popped off and deleted.
hg qref -X *
hg qpop -f
hg qdel <patch>