I just changed the pump tank the pre set pressure is 100 psi and the pump gage reads 50 psi and the water is running fine will it make my pump break down if I don't lower the pressure?

Something isn't right here. Never seen a pressure tank pre-charged to 100 pounds. Lets have some more info here and we will try to figure this out. If gauge is right, and tank is truly charged with 100 pounds, you would be having problems with pump cycling.

I just changed the pump tank the pre set pressure is 100 psi and the pump gage reads 50 psi and the water is running fine will it make my pump break down if i dont lower the pressure?

Is this a bladder or a pressure tank? More details please. Brand of tank? Model number? It sounds like a galvanized pressure but don't fret. If it is, indeed. A pressure tank the pressure will equalize itself with use if it hasn't already. Regards, Tom