I reckon this one has been mentioned before but I just can't remember the resolution: if you remove the locking ring from an Opinel, is that enough to make it legal?
Yep, as it can no longer lock.
I wouldn't use it that way to be honest. Opinel has almost no friction to hold blade open and I had mine almost fold several times on me when I didn't lock it.
it very much depends on the individual knife. Some are very tight and act well as friction folders, others will flop about and would be very dangerous without the locking ring. You can gently mod them to act in either manner, whatever your preference is really.