Save transition

[Vincent Rosati]

Canopus Video Effects is a plugin that has enhanced transition controls.
But, if you want to make your own custom wipes/transitions you could create a greyscale image in PS or greyscale video in After Effects.
I once created an animation in Poser, than saved a movie with an Alpha Channel, extracted the Alpha and used it as a transition in Premiere.
Basically, once you have your Alpha (greyscale) video layer, you might apply Effect/Alpha Adjust:(perhaps)Invert and/or Mask Only.
Than you might apply Effect/Track Matte Key to one or both of the main clips, and set both layer’s Alpha targets to the greyscale layer.

I’ve also used Luma Key Track Matte for this type of situation.

It takes some playing around, but these effects should get you moving in the right direction.