You can safely use palette rework outside of FEbuilderGBA, you just have to use SkillSystem Custom Build (I don’t remember the exact name by not using FEbuilder anymore) the problem that every time you edit the classes you will have to re-run a custom build to associate the new ones palette, it’s not difficult, but it requires a lot of patience and you need to have a minimum of knowledge on how to use a Buildfile.
personally if you want to continue using FEbuilder, I advise you not to use this method which in the long run becomes a considerable effort, and at this point it is worthwhile to switch to the buidfile