Blackmail? I think not.
Dear Dreadnaut: You state what I am discussing with Samarui would be extortion or blackmail. The definition you use describes such acts as an attempt to obtain money or something of value. Neither money, nor something of value, is being requested in that scenario.
black•mail (blăk'māl') n.
1. a. Extortion of money or something else of value from a person by the threat of exposing a criminal act or discreditable information.
b. Something of value extorted in this manner.
It is NOT extortion or blackmail to simply advise the Lender of the N/O/O status of a property secured by a Deed of Trust specifying it to be an owner occupied property.
The Lessor is not requesting money, however, the Lessor is making it clear to the Landlord that attempts at bullying him further, may result in their being quite busy over the next thirty days in attempts to obtain a mortgage refinance, or earn thirty thousand dollars to pay off that loan if the Lender were to call it in as a result of discovering a fraud.
But the Lessor is NOT attempting to obtain money or anything of value for him or herself, thus your argument that doing so would constitute extortion or blackmail is incorrect.
Granted most trial lawyers would argue such an act would constitute a civil tort, HOWEVER, the fact remains most Plaintiff lawyers work on a contingency fee basis in such matters.
Being that not much money from a civil court judgment could be collected from an average college student renting a house (being that an average college students' gross assets usually amount to a couple of cinder blocks bookshelves, a cable spool dining table, four folding chars and an eighty dollar television set) I wouldn't be too concerned with a Plaintiff lawyer agreeing to take on a civil suit in such a matter with such little chance of recompense.
Coupled with the fact that it is very, very doubtful a jury could be persuaded to find for a landlord engaged in bullying tactics, I really don't see much of a problem for anyone but the Landlord.
The best thing for a landlord, who does not want their Lessor to be able to protect themselves against intruders, is to address the firearm issue up front, in the written lease agreement previous to signing one.
And if they recall signing an owner occupied affidavit at their purchase loan closing, and their note contains a "due and payable" clause which might allow for the Lender to call the note in within thirty days if the property is not owner occupied, it might be a good idea to either not "go to war" with their Lessor, or they might consider refinancing the note with another mortgage lender as a "Non Owner Occupied" investment property.
If a clause in an existing lease agreement does not exist barring a Lessor from keeping guns within that property, it would probably just be best for a Landlord to simply not bully a Lessor simply because of an "anti-gun" bias.
Then, when the lease is up, re-write it to agree up front that anyone leasing the property will not be able to keep and bear arms within that property during the term of the lease.