Rightó that's what had to be done with the Mini-Cobra locks I just got, to fit 1-3/4" oarshafts with a 3/16" rope wrap (about 2-1/8" total diameter).
I don't recall whether the full-size Cobras had to be opened up to fit Carlisles (1-7/8" shaft w/sleeves) but I did have to bend the tips inward.
The starting point is to put the oar in the lock and see how it fits. For the Cobras, Sawyer recommends a bit of clearance at the bottom of the lock. I think the standard-type locks (strong, superstrong, whatever) are supposed to fit the oar evenly around the bottom and sides.