ToolProgression doesn't work period in the latest Forge 1.12.2 version. Doesn't crash, just doesn't function.

Mod appears to work in Forge 14.23.5.2820 to 14.23.5.2830 and 14.23.5.2840, but configs can't reload in versions 14.23.5.2820 through to 14.23.5.2830, tool mining speed doesn't change (not sure if its supposed to or not)
Tools still work for their original purpose (axes changed to shovels will still work on wood, etc)

Unsure of a version of Forge where the mod functioned as intended, might need to test it.

It works fine with an even newer version than what you're listing in my personal 1.12.2 mod pack. Maybe you have some other mod interfering with it or something.

Hm, interesting.

Maybe you have some other mod interfering with it or something.

See I thought that at first too. I tested it in several fresh installations, with different Forge versions, both with and without additional mods, (just in case, reinstalled Minecraft entirely in case something broke) and it still didn't work for me, that seems to rule out mod conflicts.
Mind letting me know which version of Forge you're running? Perhaps CurseForge launcher isn't listing it as latest.

axes changed to shovels will still work on wood, etc

Wait... I didn't catch that earlier. So you're trying to make an ax to a shovel? This might not be possible, because some stuff is just way to hard-coded. ToolProgression works when you're trying to change the mining levels for tools and blocks. I'm not sure if replaceing the tool-type ever worked properly.

I'm testing it with forge 14.23.5.2836 and 14.23.5.2854 and harvest level overwrites are definitely working for me.

For funsies, I also made an iron shovel to a pickaxe:

And sure enough, it works fine. Though WAILA says it needs a pickaxe, but you can harvest just fine.

In contrast, a diamond shovel doesn't work:

Either you're doing something completely wrong, or some other mod breaks stuff.

*edit: But for fucks sake, 1.12 forge is so slow, I can't stand it anymore.

Ah, I see where the miscommunication was.
I do recall several months ago (likely in older mod/Forge versions) changing tool types working near perfectly fine, even for non traditional (vanilla type) tool "types" like "gallagher" or "knife". Rarely had issues there.
This doesn't seem to be the case anymore, which is why I opened the issue.

Weirdly enough, the '/toolprogression get' command will accurately report any changes made to a tool, will show the changed tool type/tier etc. It just wont function as such.

Additionally changing mining levels and such wasn't working either iirc. I'll have to test again to confirm. In simplest terms, the mod doesn't appear to even work for anything. Which is baffling to me if you're not having issues with it at all.

I don't want to just come along and say "mod doesnt work, haha fix"... Well aware that's not fun to hear, and definitely unproductive.
Not sure where to go from here.