The Pope is still in charge of all 22 existing rites. Not sure how this would be different. The major problem I see would be to which Rite the priests would belong. I do not know if a priest of one Rite can serve the Liturgy (mass) of another, but I suspect so or at worst an indulgence (hope this is the right use of that word in this sense) could be granted.
Yes, they can offer the Mass in (for example) the Ordinary Form of the Roman Rite and the Maronite Rite, (that's called being bi-ritual), provided certain conditions are met. They have to first receive permission from both bishops (the Roman bishop and the Maronite bishop), and be "granted faculties" by those bishops. They must also be familiar with the forms / formats of both versions of the Mass / Divine Liturgy, and for the Maronite Mass, it is my understanding that part of their liturgy involves the use of Aramaic (the language of our Lord), so they would have to be familiar with at least some Aramaic.
One priest who is bi-ritual in both of those rites is Fr. Mitch Pacwa from EWTN.
Here are two video clips, the first being part of the Daily Mass in the Ordinary Form of the Roman Rite, and the second being (I believe) part of a Daily Mass in the Maronite Rite.
| Part of Ordinary Form of the Roman Rite Daily Mass Part of Maronite Rite Daily Mass |