A few thoughts based on the catechism:
2559 “Prayer is the raising of one’s mind and heart to God or the requesting of good things from God.” But when we pray, do we speak from the height of our pride and will, or “out of the depths” of a humble and contrite heart? He who humbles himself will be exalted; humility is the foundation of prayer, Only when we humbly acknowledge that “we do not know how to pray as we ought,” are we ready to receive freely the gift of prayer. “Man is a beggar before God.”
2111 Superstition is the deviation of religious feeling and of the practices this feeling imposes. It can even affect the worship we offer the true God, e.g., when one attributes an importance in some way magical to certain practices otherwise lawful or necessary. To attribute the efficacy of prayers or of sacramental signs to their mere external performance, apart from the interior dispositions that they demand, is to fall into superstition.
2562 Where does prayer come from? Whether prayer is expressed in words or gestures, it is the whole man who prays. But in naming the source of prayer, Scripture speaks sometimes of the soul or the spirit, but most often of the heart (more than a thousand times). According to Scripture, it is the heart that prays. If our heart is far from God, the words of prayer are in vain.
Whether/how you choose to pray, the purpose is raising your heart and mind to God. You can pray the Divine Mercy Chaplet “perfectly” in terms of form and the words or the Rosary or any other prayer and it is pointless if your heart and mind are from from God. So, the motive for modifying a prayer would really determine whether your modifications are for the purpose of better raising your mind and heart to God in the group setting you describe.
Thinking that certain prayers have a particular power/authority/effectiveness out of the mere human words vice what is in your heart is bordering on superstition. Just my .02.