Custom keycaps are limited and very expensive. Modding with landing pads is a bit of work since you have to disassemble the entire keyboard but it's not terribly difficult, just takes some time. You can get landing pads and topre keycaps from Elitekeyboards:
https://elitekeyboards.com/products.php?sub=access,slpadsYou can also lube the plastic sliders. Should be a guide or picture of where to lube on the forum somewhere. I think that's the extent to how much you can mod a Topre keyboard besides swapping parts between different Topre keyboards in case you want 55g or Novatouch MX sliders in a board that doesn't have such features. All of these require the disassembly of the keyboard; you don't need to take apart the keyboard for swapping keycaps.
Edit: Look for spiceBar's Topre modding threads on this forum. You can also PM him, he's pretty active on Topre related threads.