I understand that the HHKB layout needs a different PCB. Does this PCB also support the regular non-split right shift and non-split backspace key? Would I be able to open the plate, remove the second hammer, put a key stabilizer insert in the barrel and use a regular right-shift or two-unit backspace key (and change the mapping in the GUI for the controller)?
The backspace is the same no matter what PCB – you can split it and it has pads for both keys, or you can keep it the 2U size backspace like what is standard on many Model M keyboards.
If you get the HHKB style right shift, the barrels and PCB pads are actually in different positions, so a regular large right shift key will no longer fit.
Both PCB designs offer the ability to split the right shift into 2 working keys. You can split the right shift on the regular style PCB but it will need to be with the 1U key on the left barrel and the 1.75U key on the right barrel.