HCA: Hermit Crab Association

I just got a new shipment of shells and noticed a triangle shaped crack on the upper lip of the pearl turbo. It hasn’t broken off but is a bit loose so it may.
Can the crabs still use it?
Should I try to repair it?
Or break off the chip and sand down the edges so they’re not sharp?

The crabs can still use it. If it is thin enough to shatter that easily though, they may choose to eat it rather than wear it! I have had that happen with pearled shells before. If you want to take the time to sand it down it wouldn't hurt anything, but they will often alter shell openings themselves (like making room for their eye stalks) so if it isn't to their liking they will fix it.