Are Owner Occupancy Agreements common?

Yes. You can try. Unlikely to get anywhere but you never know and you may be able to soften the terms (permitting subletting for limited periods of time perhaps). If that is an important term you need to shop it around before you agree to a commitment.

I have seen owner occupancy - after all you get a better rate if it is your primary ... but I have not seen the clause that states they can raise the rate if you stop occupying the home.

Get a new bank, because once you ask them to take that out, they are going to think you are not intending to use the home as a primary.

I've seen this for second-home mortgages, except that it absolutely forbids renting out the property for the life of the mortgage, or requires lender permission to do so. No predetermined upcharge or fees.

Traditionally, conforming primary loans were allowed to convert to investment after something like 6 months or a year -- whether specified upfront or by permission granted by FNMA, I don't know. And then those same owners immediately got a new conforming FNMA loan for their new primary, possibly counting the estimated/appraised rental income on the first house to qualify. And so on.

I think few people pay attention to StreetEasy's Talk categories. If the thread title had indicated "mortgage", I'm sure one of the helpful mortgage-officer regular posters would let you know just what the current guidelines are. If you start a new thread with that in the subject line, you might also want to indicate the type of residence, and the approximate mortgage/purchase amounts, so they can give you specific advise.