Welcome to Alaska!
Going from an E85 tune to 90 will be a considerable difference if the E85 tune was even slightly aggressive timing and fuel wise.
If you did have a truly tuned E85 setup then putting just 90 in the tank will cause the car to run very rich and potentially cause issues. E85 requires a considerable amount of additional fuel flow over regular 90.
Your car is able to re-tune the fueling automatically up to 40% in some cases however this would only be for idle and cruising (closed loop mode). Over time it would make some changes to open loop as well but it will never run correctly. You will also get a check engine light for the ECU having to make such massive compensations. When you go under med-heavy throttle it will just go very rich (black smoke, hesitation, etc).
Most local tuning shops could set you up very quickly with a basic tune to get you around until you are ready for something with meth/water or something more performance based.
Again welcome to the group! Great bunch of people around here.