This is what I did to mine:
Had a white type-s and a black non-printed, swapped the Type-S sliders and rings into the black non-printed.
Got haku's PCB and customized the TMK firmware for it (+ bluetooth)
Added a battery that sits inside for wirefree usage
Made holes in the housing at one point because I swapped sliders with novatouch MX sliders (so it's ready to be swapped to that again).
Swapped domes from a Realforce 87u 55g.
For decor, added some golden metallic stickers (TypeS + HHKB Pro2)
Pretty happy with my hhkb... it's the endgame 60% for me. Did something very similar to a FC660C feels nicer than the HHKB because the switches are plate mounted.