>   Do the scripts even handle a R14->3513 install?

Nope.

At first glance that would be beyond the scope and intent of project goals. Then upon reflection I thought, why?

No good reason. In an ideal world I suppose we should support both directions. I'm sure there will be users who will test R14, say WTF for various unexpected problems and want to revert to 3.5.x.

A temporary fix would be for users to copy both scripts (migratekde3, r14-xdg-update) with new names (restorekde3, r14-xdg-restore?) and then reverse all of the replacement snippets.

Somebody who is a script wizard could revise the existing scripts such that users could use the scripts in either direction.

Darrell