I’ve managed to open a Pilot 2+1, there’s no complicated or secret gesture, just brute force: pull the central section apart from the body (it is held by friction). You don’t need to remove the clip, which is good news since it’s quite a complicated assembly (with two different springs!) The internals are then free to slide out for your viewing pleasure (if you happen to be a multipen geek, that is).
In order to adapt the eraser module, one of the pen tubes has to be modified a bit but that’s all there is to this mod.
And the obligatory family pictures:
