a) Preparing the door for the 2 1/8-inch-diameter hole, which is larger than what is allowed as a job-site preparation by NFPA 80. This may be allowed as a field modification by the listing laboratories with prior approval.
b) Filling the existing mortise pocket to maintain the integrity of the door. This is especially problematic on wood doors. I have witnessed several wood door fire tests and I believe this void would cause the door to fail.
c) Covering existing holes from the mortise lock. There are conversion kits available which cover the face holes and fill the 86 edge (scalp plate cutout), but I don’t know of any that have been listed for use on a fire door.