We can add something to let the player re-lock the door, but to get back in they’d need to pick the lock or force the door with a crowbar again. Just because they opened it once doesn’t mean they can open it again on demand. You’re right that we simply replace the “locked door” tile with an “unlocked door” tile.
We could probably add keys somewhere in the house though, or elsewhere for that matter. It would be nice to reward carefully breaking in instead of smashing your way in.
We could add keys, the key would say which door it unlocked instead of the other way around.
In fact, it would probably be reasonable for there to be one key per house, that wouldn’t be much harder.
