I cannot because I'm just a goofball with a mild interest in home improvement
Wikipedia says HEPA filters became commercially available in the 1950s though so anything older than that I'd bet some beer money would benefit from a less dense filter
I wouldn't think forced air heating systems that old are too common though tbh
There's potentially a rule against it depending on who you rent from (idk w/ my current landlord corporation, would have to ask) and if they're feeling particularly vindictive they could try to use evidence of your "unauthorized repairs" to withhold security deposit.
ymmv depending on how sneakily you can replace an air filter
We just didn't use a filter at all in our last rental. I know it's bad for the ducts, but the landlord was an asshole, and I wasn't about to spend my money to protect their investment.