who do you call to put a timed thermostat and a lock?

there is a lockable cover you can gte to put over it,

at most major stores

There are many options, I prefer the steady temperature ones that come with different temp settings (you install it and it keeps the temp steady at 68, 72 etc) There is no way an employee can change it as there is no dial :) You should be able to get any style at a hardware store or you can call a HVAC company.

If you have a furnace see what company it belongs to. Maybe they could come set that up. If not I'd look in the phone book for places that install heating and cooling equipment they should have no problems doing that project for you.

get both at home depot & Lowe's.....you can be sneaky & put an "acustat" in the return air & no mater what the setting it cannot over ride the accustat.