You'd probably not even need to do anything to the can wiresOBD port switching isn't delicate. They are just wires, as long as you don't cross them, then cutting a wire and putting a switch in isn't going to cause a world of problems any more than the connectors on each end of those wires.
Best to look at the Pin out for the port and pick an appropriate wire that would isolate the lines that carry data, rather than power or ground.
Something like a Dip switch would be perfectly adequate. A micro switch tends to be a momentary switch only making contact when pressed, so maybe not what you want.
I know several people who have done this with no ill effects.
Even then, this doesn't stop someone lifting it and the majority of these cars are stolen for parts, if they can't get it to start it will become a parts car pretty quickly anyway.
I remember in my LandRover days the LandRover magazines used to have adverts for a post that you would concrete into the ground then you would literally lock your car to the post to stop someone moving it off the drive.
The 12v feed to the obd port would likely be enough and not likely to cause can issues as the 12v is usually fuse protected and I doubt the ob port fuse being broken would cause serious issues