That’s very kind of you, here are some screendumps of the transition I made manually (I hope this works):
Here’s the first clip.

First clip slides to the left half (arrow) and resizes to 50% width, meanwhile second clip dissolves in:

First and second clip co-exist:

Second clip gets larger to 100% and slides in from right (arrow), meanwhile first clip dissolves to background:

Second clip is at 100%, end of transition

Does this clarify the description enough?
As you can see, it is perfectly doable manually, but maybe not for 500+ transitions 😉
So any ideas (a faster method of copying this process is already better than doing it completely manually) would be greatly appreciated.