I don’t think you can do this without also adding a video transition en masse, so if that’s a problem, just set your default vid transition to 1 frame. Here’s what you do:
1. Select everything in the timeline
2. Drag up to the canvas and hold until Insert/Overwrite/Replace Etc. overlay menu pops up
3. Drop it on Overwrite -> with Transition.
This should replace everything in your sequence with what you have set as the default transitions.
I don’t know if I explained that well but it’s a good technique to be aware of. Let us know how it works for you.
Cheers,
Stace