They would say from a legal standpoint they are not taking your property, they are just modifying eviction laws. 

Their leases are state-specific (which is standard these days) and can be modified

I thought I read somewhere about adding a clause that the seller will not extend, modify or otherwise alter the existing leases in any way ( I can't remember where I read this). 

I sent my normal residential lease agreement to my attorney and he modified it to implement the following:1.

If you accept, the entity that you are requesting information from has 30 days to comply and fulfill your request from the date all monies are paid and you have answered any/all questions they have about your request.If they deny your request, you are more than welcome to submit a modified request.

And the leads you can't get in touch with updates info every 36 hrs.also has contracts you can modify.

They can generally be called by the bank or modified at will.  

I am in the process of getting an REO under contract through Fannie Mae, and LAST MINUTE they sent me this bogus Real Estate Purchase Addendum that TOTALLY negates the terms in our agreed upon offer.....My agent is telling me its "standard" - but I am refusing to sign unless it can be modified in a way that doesn't contradict VERY IMPORTANT TERMS in our agreement.

YOU should be the one to determine your market and whether or not it is profitable to take that loan or modify the terms.

A basic HI doesn't know framing and may not notice a modified truss in the attic for instance, but that is an important and costly repair.