Hard to say as I don't quite remember a lot of the changes. A good while ago I do remember looking through them and I think there are also some undocumented changes (I know the 1.7's excuse of a change log hardly displays any of the changes at all).
While I did try to fix DKII's issues where I could, all of my changes are things that can be done in the editor as I change configuration settings and Level Variable settings. So certain hardcoded changes from the 1.51 patch can't really be replicated. That being said, the amount of things I'm capable of doing with what is technically an unfinished / broken editor is quite outstanding in and of itself.
One of the things I did with the patch was recreate the campaign with a lot more difficulty than before, so you'll be getting that either way. DKII was originally designed to be an incredibly easy and casual game, hence such design choices like the Heal and Lightning spell being very powerful and cheap so spammable. My patch does a lot to change the game from this direction, instead aiming to expand the game's features and design it better for higher skilled players.
I've made it up to Level 14 in the patch, technically, but I don't believe I released anything beyond Level 11. Levels 12-14 were never fully tested and Level 14 had a few technical issues as well. The
3.0 patch includes levels up to 11 (and Levels 12-14 are designed around the 3.0 patch). However, the
3.5 patch released three months after includes a lot of major changes but only includes Levels 1-5. I heavily revised those maps to significantly improve them around the new patch, and levels beyond that haven't been properly adapted yet so I consider them unplayable until I update them.
That's pretty much where I'm at, but it'll still be a while as I'm following this trend of revising old map designs from scratch where I feel necessary.