2000 Mustang GT Predator Tuner question please help!

I was wondering... Due to the economy and gas prices, I was thinking about changing back my Predator Tuning to the stock 87 Octane tune from my current 91 octane tune. I have been running the 91 octane tune since 88k miles when I got the new motor directly from Ford. I am currently at 122k and I was worried that since my new(ish) motor has ONLY been running the 91 tune since new. Is there a risk if I switch to the lower octane (stock) tune and switch from 92 octane gas to regular unleaded??? Thank you very much guys, would like to hear both sides if possible.:SN:
 
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