You're correct, an E0, E10, E15, E30, E44, E85 etc tune will have things like stoich fuel values change to accommodate the change in actual stoich. This is a base lookup for many items like cranking fuel quantity, transient fuel, cold start enrichment, and dozens of other fueling tables. So this is like the first thing ever that should be changed. We have seen people simply turn off the error reporting for fuel trims, which is also weird because that takes fare more work than doing it the right way. Now the real scary thing is by not making proper adjustments for ethanol content you're making the o2 sensors do all of the correction, but this means the engine has to be lean first, and then the o2's correct to bring it back to commanded lambda.