Here's an excellent video from an attorney with decades of auto related litigation experience and his explanation regarding Magnusson Moss Act , vehicle mods, warranty denial etc.
It is slightly wordy and 17 minutes long but well worth watching until the end.
He perfectly describes what you can expect from your dealership and how you are truly placing yourself at their mercy regarding any mod which might remotely cause or contribute to your service issue.
Even if you're right... You still lose.
Don't count on breezing into the dealership waving Magnusson Moss like a battle flag.