Leasing agreements are changed unilaterally all the time, unless the contract provides for mutual agreement and consent to any changes. The property owner, for example, can raise the rates, start charging for parking, etc. with 30 days notice to the tenant unless the contract provides for longer notice provisions or that changes are only done at the renewal of the lease. The tenant has the option of accepting the terms, negotiating different terms, or moving out. You could argue if the prohibition of explosives on the property owners property is a 'drastic changing of the conditions', or is it an urgent action taken to protect the property of the owner?
If an apartment owner discovers that a prepper has his spare bedroom full of 25 five gallon jerry cans of gasoline, would you expect the apartment owner to take no action or to prohibit such activities? Would your opinion change if your children's bedroom was directly above the prepper's spare bedroom?
I have no doubt that some people are foolish enough to sign a contract without reading it, and I personally know that some leasing agreements are as shoddy or sleazy as you say. Most respectable leasing agreements do not allow rate hikes with short or no notice. They're usually rolled into end of the year or end of lease interval.
Regarding explosives and large amounts of gasoline, most leasing agreements do not cover these. Because they are covered under fire code and local ordinances. I had an explosives license and was one of the two leads on explosive storage at a site in Sikorsky, which became the model for all Sikorsky sites. So I know more on this than I would like. Explosives storage must comply with BATFE regs, federal law (typically have a license and follow BATFE regs), state law (usually see federal laws) and local rules (these can get interesting quickly). Some locations ban any explosives, others say just follow BATFE regs. If large quantities of gasoline indoor storage in residential rental properties was legal and in compliance with fire code, then yes, it might be the place for a lease to cover.
Nearly all leasing agreements do say that illegal activity and activity in violation of fire code are banned, and subject to termination of lease. I fail to see any problems with that. As a risk management expert, you'd probably tell a client to do the same. To avoid lawsuits, bad PR, et al, stick to "Illegal stuff is bad, so don't do it on our property. If it's legal and not destructive to our property, not our concerned."
So, no, children (mine or anyone else's) would not change my opinion.
