The Practice of Tatbeer
Question :

Is the practice of Tatbeer (striking swords on the head, slitting it open to stream blood) permissible?

Answer :

As the act of Tatbeer and other kinds of symbolic actions are performed to propagate the right principal and express emotions towards it, then it is religiously recommended from this side. Yes, it can be prohibited because of secondary reasons, like if it causes prohibited harm, public disadvantage or other similar reasons. There is no set criterion for such prohibition as it differs from place to place and from time to time. It can also be different because of difference in personal perspectives.
We ask Allah Almighty to guide us and all devotees in all of that as we only depend on Him.