If you add or remove geometry below the unwrap-modifier you will loose all edits done in UVW-unwrap.
There are 2 solutions for this problem:
1) Make your changes in an editPoly-mod. above the unwrap-mod. and continue uvw editing by using another UVW-unwrap mod. on top of that. (Later you can collapse the whole stack into editablePoly.)
2) Collapse the stack to editablePoly, make your changes, add a new uvw-unwrap and continue your work.