Lease issues aside...
I'm going to be renting a townhouse for the next 1-3 years.  It's got the same cheap Kwickset locks (or something similar) that every builder buys.

Are there any locksets / deadbolts I can buy to replace those locks WITHOUT modifying the door or jamb?  I can work a deal with the landlord to change the locks (and change them back again when I move out), but I won't be able to drill new holes or over-drill the holes that are already there.  I need a drop-in solution.

My reloading / gun room will be at the back of the townhouse along a tree line.  There is a door to the back "yard".  This area is not prone to break-ins and is VERY close to a police station, but I still feel the need to up-armor that entry simply due to the contents of the room.  While I understand a determined thief can get by ANY security measure I put in place, I just want to do my due diligence and do the best I can with what I have to work with.  I also understand that this is just one layer in my overall security plan...

Thanks!

Just have a locksmith rekey them. If someone else is home take them to the smith and they will do them for a few bucks.
Have a spare key for the landlord.
For the back room.