I like the safety suggestion but think you are probably OK here. Whatever the oven takes, if the circuit breaker doesn't pop (and your house wiring is "code"), the total amperage is below the trip point. If you don't think your wiring is up to code, all bets are off.
When you first turn the oven on, the burner runs full out for at least 15 minutes before reaching cooking temperature. You said the max temp before any modification was almost 700F. Electrically, ramping the temperature up to 700F in 30 minutes is no different from running the circuit at any other temperature as the amperage through the line is the same.
Nearly all products are engineered with a safety factor. I'd guess this has at least a 20% safety factor, probably a lot more, given the inaccurate thermostat they use. Quick math suggests you are OK to 840F-ish.
We modified my buddy's cecilware to run much hotter, but his oven is outside. I did take things apart to do the "tuning" and noticed that the insulation wasn't the greatest, but he is always around and really doesn't run the thing more than 750F (800F tops a time or two).
What we did find with his oven was that the stone temperature varied greatly as the areas right above the electrical heating element were something like 50F hotter than more remote areas. I used metal lath (used for building construction) cut to the exact dimension as the pizza stone and used it as a 1/8" spacer under the stone and on top of the metal pan supporting the lower heating element to even out the heat. It worked great and you might need this as well.
If this is a 110V, flimsy construction product, take more care. I don't know this product. If it is more of a commercial grade product, which the 700F seems to suggest, be careful, but you are probably OK, IMO.