The only locks I know of that can be combinated for a door key are those with removable cores. Best and Falcon come to mind as I am familiar with both from my Facility manager days. There are even drawer locks and cabinet locks that take the cores. As a FM I inherited a facility here we had around 500 different keys we stocked blanks for. In three years we witteled that down to 50. We stocked combinated cores for master and submaster cores. 2 seconds to rekey a lock.
Ron
I've used one of these basic locks, to secure a spare tire on a Jeep; bought the one with the integrated cable loop.
Home :: BOLT Lock
Easy to "program" (no pulling the core), and so far, reliable. I like the convenience of having it sync'd to the vehicle key.
Rgds, D.