I don't know if there's realistically a bulletproof way to solve the underlying issue - which imo isn't the exposure of the account id, but is the fact it can reveal which other characters are mine. With the underlying goal being to block all my characters from being visible or being able to interact with someone, theres always going to be a way to figure that out - maybe slightly harder than this tool using account id, but not by much.

Ultimately there needs to be better tools for reporting and dealing with harassment because even with a theoretical bulletproof blacklist nothing stops a bad actor rolling a new account