Basically, the tune (OEM or aftermarket) is adjustable, but not infinitely adjustable. Every fuel has its own stoichiometry. If you add a very small amount of a second fuel to your primary fuel, the PCM can accommodate, using the A/F sensors. Note the simple case of adding HEET to the fuel tank. Same basic idea.
But at some point, if you mix in enough of that second fuel, the PCM will be stymied with regards to what to do with this new mix. And this is true whether or not the tune is provided by Ford or by a tuner. In fact, once the car is tuned, the flexibility that the PCM had with the stock tune is gone, you have greatly narrowed the operating parameters. That is the whole purpose of tuning, to gain greater power with greater responsiveness and greater efficiency.
So, you COULD spray a very small amount of methanol with no adverse effects while untuned, but whether it would be beneficial and to what extent, IDK.
