I have a similar clause in the lease...
Never had a problem with them telling me to stop, and I'm frequently doing something. Front brakes, water pump (that got a bit messy), alternator, etc. I try to clean up well, afterwards, too.
I have even had a couple of the maintenance guys come over and ask what I'm doing, dispense some advice and swap auto repair horror stories...
I have a good set of cheap (pricewise, they seem to actually be good quality) tools that fit in a plastic case I can tuck behind the seat. Got the set at Costco for about $50 7-8 years ago. I'll look at the manufacturer's name, if you're interested.
By no means a complete set, but as I need something I'll go out and buy it. I have two .50 caliber ammo cans behind the seat as well, one with tire chains and the other with the miscellaneous tools I have collected. Got a pipe wrench, a huge crescent wrench, and a fan wrench set back there, too.
I wouldn't attempt to swap an engine or tranny in the parking lot though. That might be pushing my luck a bit...