I used the wrong key in a 5 lever mortice lock causing the ant i tamper mechanism to swing down preventing the use of the proper key. Can I reset this or do I need a lock smith? Thanks.
Try a small screwdriver in the top of the keyway. Just turn the thrower back until it clicks into place. On most locks it will not revolve all the way, do not force it.
If not look for MLA or ICL locksmiths.