First time opening an HHKB I lost a spring (never found, a donor board is still missing one). For HHKB one of the issues is the domes are barely glued on to the PCB so aligning the top with the domes, getting the domes to sit flush when the springs are under them, or having the domes stay where you put them can be a real pain. RealForce uses stronger glue so that becomes less of an issue, unless you take the domes off on purpose. Everything else is trivial in terms of difficulty so if the domes are in one sheet it shouldn't be a big deal. Just don't lose springs! I've never been able to find replacements.