Hmm… That shouldn’t be possible anyway - I own all the variations of blastoise186 on this community by just having this one account - so no-one can register Blastoise186, blastoise186, BLASTOISE186, BLastoise186 or any other upper/lower caps variant because the system will consider them to clash with the existing username for my account. The system already blocks any attempt to do so and will just tell the new user to pick something else.
If it’s not doing that for you, there might be a bug somewhere, so you’ll probably want to have Support take a look at your instance.