Pretty sure you can KOS for this and if done continuously warned through rule 2.4a Constant T-baiting as Innocent/Detective? Why should it make a difference if it is done preround? It's still T-baiting which can be done by all roles so as long as they don't turn into a Detective you can kill them.
I dont think KOSing them makes much sense to be honest as performing a traitorous action before you get your role does not indicate that you are a traitor only that you are a bit of a dick. I think its more accurate to call this loopholing the t baiting rule to try and ruin the game for people who want to use the tester/collect diamonds and not get punished as it was only pre round.