Reading with interest, the Office Squatter thing, as I call it:
I did that, staying 5 years in spite of the downsides. A decayed downtown but did have stores nearby, within walking distance, plus I was working a day job nearby. Some of the better aspects, of a 'skid row' neighborhood was that I could work late, making all kinds of noise (no residential neighbors).
The 'street crime' nearby was bad...but nowhere near the decay there today.
I believe it's the Fire Dept. that has the biggest worries, as any commercial building should not have a situation that endangers the Fire Dept. personnel, as well as any office tenants staying there.
Blocked the windows off, which got noticed. You have to live a kind of 'half-life' in that there was no shower, or proper sink for food prep.
You are not accumulating a valid renter history during your stay, which could hinder future renting qualifications. I used a mail service.
With any groceries, I would enter through back entrance, with groceries stashed in a box.
A bigger hazard, than getting caught by Fire Marshall was getting spotted by some METH FREAK, who can think (he) deserves some hush money...if he is smart enough that is.
I benefitted the building in the consistent mock-ups I performed at night, and sometimes even insisted that some intruders leave the building, there at 2 am. (More meth freaks).
Currently that would not be a safe challenge to make, there alone with a strange, homeless weirdo.
All in all, it's not living, really, only more like a temporary respite, until a real residential rental becomes possible. I did get my 480 pages of Patent application completed and sent to USPTO.
Many stores, now are boarded up or occupants are sometimes without actual, locking front doors...full of useless junk, and shoppin carts.