This is my personal opinion, therefore I could be wrong. Irreverent modern piano music in Church is not pleasing to God and is not appropriate to liturgical rites.
I’ll believe that when God Himself says so. I doubt very much if you are God’s spokesman.
If your opinion has been formed through sermons, I would respectfully suggest that sermons regarding the Lord, Scripture, faith, morality, etc. are far more appropriate topics for homilies.
As for the Holy Father, he also is not God’s spokesman with every word he utters, only in infallible statements. He has made no such infallible statement regarding music, and thus speaks from him human preference for certain types or styles of music.
As for the OP’s claim that the priest was “changing the words,” I would have liked him/her to have given an example. Is the priest really changing words (and Lord knows enough of them do

) or was he using one of the many legitimate options available in the Sacramentary?
As for the OP’s claim that the Mass was “irreverent,” maybe it was, but it does not seem so by the way it was described. Many “traditional” Catholics scream “irreverence!” just because something is not to their liking (i.e. the music - example: the use of a piano… NOT irreverent

; a piano playing a secular tune as in a lounge or bar… irreverent :nope: ). Just because one person doesn’t like something doesn’t make a Mass irreverent. That’s as subjective as saying, “I love broccoli!” or “I hate broccoli!”