I've only been using svn @ $work and never really got into it, so thanks for the extensive explanation. I've read all the thread in detail, and followed the links provided. Many interesting ideas here! Hopefully, I'm learning something.
Regarding the specific issue being discussed here, since versioning control systems keep track of what's getting modified anyway, it seems strange that there's not a "selective" cp command that will copy one branch over another without overwriting files that have been modified in the destination one. If there were, then the OP would issue it before running the tests, resolve problems, and then merge.