Yes, I am fully aware of that. I do not think there is any plausible scenario where Pope would wake up and single-handedly change Eastern Divine Liturgy. You state Orthodox belief in great way. This is however not East vs West ecclesiology- it is simply about Catholic vs Orthodox ecclesiology.
In Catholicism, if Pope is to protect integrity of Church as Vicar of Christ, he can exercise his power. For exercising his power he is accountable not only to God, but also to entire Church. Papal Oath included such phrase before it was relinquished, but it stays true even if not stated. God judges all our sins. If you have authority and you abuse it, your sin is greater. If someone follows you in good will, he has no sin as fault is not his own. Good will is however, very important there.
From Catholic viewpoint, Holy Spirit has authority to speak through Pope to change Divine Liturgy. However, such statement would need to concern faith and morals. Because Eastern Liturgy could not have been wrong as it was and is liturgy (one of liturgies) of One True Church, and Liturgies are center of worship, and Church is infallible, bottom line is that it would be unreasonable to think Holy Spirit has any will to change it, or will have such will.
If, however, hypothetically, some Eastern synod changed their liturgy and would include heretical or immoral elements, Pope would have authority to revert or revise that change. Simply speaking Pope has no authority on his own- he only has authority to proclaim what Holy Spirit shows him to speak, and to protect what Holy Spirit has entrusted the Church in any way. Same scenarios would apply to Latin Liturgy. Papal authority exists to protect Church, not to limit it. It exists to protect Eastern and Western Catholics, not to limit them.
What people often forget is, that many Popes pre-schism (and therefore post-schism it may happen too) were Eastern. If there was Eastern Pope, he should have authority to change Divine Liturgy. Argument for Pope automatically become Latin-Rite as he cares for diocese of Rome is easily dismissed by fact many people have ordinary of other Rite who cares for their diocese or eparchy, but in the end even if that were true Pope would still have immense knowledge about Eastern Rite. Pope is omniritual by default.