PD2 gameplay code was purely LUA, so it was easy to take a copy to the old function and overwrite.
PD3 gameplay code is split into two domains, the c++ domain which is the x64 assembly that runs most of the game, and the blueprint code which is a UI based programming and gets handled as if it was a VM.
It is definitely possible to recreate something like BLT but given that you working with assembly and not lua, you need to know the number of parameters and their types before you can hook it. This is why a generic solution would be a bit hard.
UE4SS contains function hooks that will be triggered after the function executes, it doesn't overwrite the function itself as far as I know. The functionality of UE4SS can be changed most likely to add such support but not an easy task I guess.

As for BreadLib, it was built upon internally shared game build, I believe developers shared those with certain mods here. You can use unreal engine with the already created uproject to build maps but some stuff won't work and you can't inspect existing maps.
You can still see other maps code using kismet analyzer but it is not as easy as seeing in the UI.
Not to mention, since the uproject doesn't contain actual code in the functions, running stuff in the editor is harder or almost impossible.