There are two ITP palettes for each type of resource - itempal.itp and itempalcus.itp, or something like that. I don't have the toolset in front of me at the moment, so I don't have the exact names.
Anyway, one of the ITP files is a "skeleton", and has all the categories listed in it, but no actual items. The second ITP file is generated from the first when you refresh the palette or load a module in the toolset. Make sure you are editing the right ITP file. I think the one with "cus" may be the wrong one, but won't have it in front of me to check before the weekend.
-Dave
[EDIT: That's correct. Edit itempal.itp instead of itempalcus.itp, then refresh the toolset. Reference, courtesy of google: https://silm.pw/down...mat.pdf?api=v2 ]