And then seek me out for 2020 amendments with a "you freaking idiot" upcharge. 

Or could they legally be added to a lease amendment listing them as "occupants" then whatever happens - the original tenant is held liable?

It cannot be done by filing amended tax returns, a different process is required.Also, neighbor, while you cannot refuse depreciation, the amount of depreciation you can somewhat control.

If you have been charging market it may be beneficial to amend your return. 

Should I ask the current property manager to amend their leases with my management company, or have them put notice to the tenants that I'll be in contact w/ them?   

If yes, you should amend your taxes because mortgage interest for a non-owner occupied property is not allowed. 

I think there are plenty of places to achieve that happy medium, especially if you are the sort of person who doesn't have to live in an ultra-hip part of the country for either professional or preferential reasons.30 was my "retirement" goal, but I've amended it to "as soon as practical" :) For me, that is $30k+ yearly "passive" cashflow, since I can personally live on that and remove the necessity for a conventional job. 

I amend a lot of returns for this.

There's usually a clause like this:EFFECT OF ADDENDUM: THIS ADDENDUM AMENDS AND SUPPLEMENTS THE CONTRACT AND, IF APPLICABLE, ESCROW INSTRUCTIONS.

You must honor the lease.However, leases can always be amended but it needs to be mutually agreed and not threatening.