I want 100mm Rebas with Crown Lockout
I can only find 120mm Rebas with Crown Lockout or 100mm Rebas with OneLoc remote.
Which would be easier/cheaper to convert to my desired configuration?
By default (i.e. nae cable tension), the remote lockout is closed (locked out), so you'd have to take the damper out and disengage a spring. I'm not sure if that would be sufficient to then turn the old cap into a lockout or not. Tbh the damper is good enough that I wouldn't be bothered.
To change the travel you'd need to replace the air spring with a shorter one and (optionally) add a couple of bottomless tokens if you're following RS's recommendations (120mm has none, 100mm has two).
Given that one needs a bit of faffing and the other an additional purchase, I'd go for the RL version. Although double check on the process of converting RL to crown; there was a thread here the other day about it, I think.