Was that the reason you had to comment out UseLocks?
No, sir. I commented out UseLocks because it appeared that when applying your method I took from the original DefLockpicking, even though the BaseHouseDoor was properly set up (with all it's necessary props, keyvalue, etc.) after the successful lock installation, it appeared that "public override bool UseLocks()" forced the door to ignore the fact it could be locked and not accessed. I'm assuming because HouseDoors post-AOS were bestowed the ability to set Access Levels on them (evident from !house.IsAosRules).
Without knowing what ruleset you're using (or anyone else for that matter), it's hard to say that this should be an included or recommended edit - unless SecuritySettings and Access Levels have been disabled for House Doors, locks are useless, and incidentally, the use of your lock installation system on House Doors. I assumed that since you took the trouble in adding in HouseDoors that this behavior wasn't intended and/or anticipated, since it completely overrides all the hard work it took to get that lock installed onto that door. I myself have disabled the "securing" via Access Levels of House Doors (line 123 I think? Comment out : SetSecureLevelEntry.AddTo(from, this, list)
. On this same note, the system you've created gives a very viable option to removing Access Levels/Security Settings on house doors and replacing it with the player-based functionality of installing locks on doors.
I use a very heavily modified RunUO release to suit a very niche RP-enforced community, so this may not be something everyone desires for their shard, but I found it was a logical thing to do for my purposes.
None the less, stellar work. This is really good stuff, Enroq.