gifs from pngs.. a few questions, starting with:

[Ofnuts]

Then retime-linked-layers.py is the best solution. You can link "en masse" by shift-clicking the link icon, whcih will link/unlink all layers. And linking most of them is linking all of them and then clicking on the few that must remain untouched.

Beyond that you can assign specific names to some layers and I can cook up a python incantation that won't touch those that match/don't match some name pattern.