Great find! Ghidra has improved bitfield support and I think you tested this too. Can you confirm Ghidra's decompilations work out all right, or does the code get uglier?

Internally I will have to provide an exception to overwriting your customised .hpp file.

When I tried creating one, everything that was not straight forward became uglier, sadly. No idea if I did it properly, though.
One check and one direct assign was less ugly, but stuff like setting one value to 0, which is implemented by value & 0x7fffffff for example, all used Ghidra support functions.

Wht is your opinion on a split situation in which we don't update Ghidra upstream but do use the bitfield in this repo? In essence, it means ghidra exports will never override the bitfield .hpp file ever again. The annoying thing is to remember that this exception exists so when looking at Ghidra code you should translate it into (the much easier) bitfield access logic.