People have free will but there are consequences to choices usually. I would think the Pope would want a consistent message. He can excommunicate and defrock. It seems like a funny way to run a church (everybody designed their own Gospel).
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1. Oh yes, there are consequences. I learned that when I was three years old.
2. He does have a consistent message: love God and love each other, which was the "greatest commandment" that Jesus gave us.
The pope isn't a RULER. He is the earthly "father" or "vicar" who continues to lead his flock. His word is gold ONLY when it comes to morality.
3. He can but there is a trial first. It's not a simple or easy trial either. It's a MOST serious event and not lightly taken. The priest in question has had to REPEATEDLY PREACHED heresy.
AND, the "Devil's Advocate" position is STILL around, even after all these centuries.
4. The Pope doesn't not interpret the words of Jesus. The Church did way back when and did it with the help of all the bishops on the planet. There were eventually TOO MANY bishops so CARDINALS were selected from the bishops.
The "new" laws, speeding, drugs, etc., are "new" sins, on the face, but...they are OLD ones, aren't they? The Pope might declare speeding and drugs as sins, but he wouldn't do that on his own. The "sin" has to come from the PLETHORA of cardinals, bishops and priests from throughout the world. It wouldn't be a shocker to ANY of us, either, as we know that breaking the law is wrong, even if we disagree with it.
The Church has preached from the same Bible, which they collated, by the way, for the last 2000 years. It's more than that, of course, because the Old Testament is EONS older.
The Protestant Bible IS slightly different. My Baptist-turned-Presbyterian friend in Texas and I compared Bibles once. There are some books in her newer version of the Bible that the older Catholic Bible has or doesn't have. I HAVE forgotten which was which.