a simple solution is to 1 pin 'all' the uv's
2 select the messed up ones, unpin them 3 select all the uv's, go to unwrap and the messed up uv's pop back in to their correct position.

The pinned uv's kind of act as a guide for the unpinned ones

A simple solution is to:

1. Pin 'all' the UVs;
2. Select the messed up ones, unpin them;
3. Select all the UVs, go to unwrap and the messed up UVs pop back into their correct position.

The pinned UVs kind of act as a guide for the unpinned ones.