Editing professions?

okay okay so im probably an idiot and missed the thread, but a quick search came up empty.

How would one go about tweaking various parts of the built-in/mod-added professions?

Im wanting to make some changes to the rouglike classes, but would like to have an idea before trying to break something…

Mod ones should be in the data/mods/mod name here folder.
Default vanilla ones should be in data/json/professions.json.