There is a phrase that shows up frequently in the various liturgical books of the Roman Rite that I wish were not there. The words are some variation of "in these or similar words". They show up in different places where the priest is told to address the congregation and say something like what is given in the book. In the book for Baptism of Children, for example, the description is so "optional" that it seems that a priest can say pretty much anything he wants (and I have seen a few Baptisms where that actually did happen).
This is what I call the "plague of improvisation". Now I know that there are some of a more liberal and modernist mind in the Church who will point out to me that in the first few centuries of the Church they did not have liturgical books and did most things from memory. I do not deny that. The problem with using that as an argument for improvising the wording in texts is that we have no evidence that the Church Fathers did this because they believed it to be the right and proper method of celebrating the liturgy. It was more a consequence of the fact that "books" (i.e. scrolls or codices) were hard to copy and costly to own. Once the challenges to different wordings between "dioceses" became apparent, they began to make sacramentaries and then maintained the practice (sort of like the fact that we do not practice the sacrament of confession publicly anymore).
There is another problem, however that I must mention. It encourages priests and bishops to improvise in other areas as well (and I have seen this often). I was the concelebrant at a Mass once and the celebrant tried to improvise in his own words the opening collect (the first prayer of the Mass). After the first line of "O God, You are just so great, and we really like You for all the, for all the, the things that You do for us..." I knew that the train had come off the rails (there is no allowance anywhere for him to change the words of this prayer). It only got worse when he did the same thing a few times in the Eucharistic prayer. It was as though he was trying to make absolutely sure that whatever he said was different from what was in the written words.
How "making it up as you go along" became a virtue, is beyond me. What most do not consider with this encouragement for "extempore" speech, is that the practice of "ad-libbing" is tantamount to being "unprepared", and to proceeding "without restraint" (as many dictionaries define it). Trying to be fair about the motivation itself, we must acknowledge the "possibility" of it being done right. It is likely the case (though not definitely) that if all priests and bishops were completely orthodox in their views (though I am not sure that has ever been the case), and if they all had a strong commitment to reverent and traditional liturgy, that permission to "extemporize" might be safely allowed. Sadly, that is not the situation we are in, and the problems are obvious when you see all the liturgical bedlam that exists in so many Catholic parishes today.
Clearly the vast majority of those priests who improvise parts of the Mass (even though the book is sitting right in front of them) do so with the intent to modernize the wording even more than it already is (and the current edition of the Roman Missal was published in 2011; wow, that is old!). It would be one thing if the priests who wish to improvise would at least spend some time and write down the different words they want to use (to ensure that it at least sounds coherent), but instead they appear to believe that "off the cuff" is more holy (though it almost always sounds clunky and confused).
For myself, improvisation scares the heck out of me. I run from it like the plague (which is what I already called it). I prefer to speak the exact words as they are written in the Missal, and leave the accountability for the words on those who made the original choices (that is their job after all). There are a few places, however, that I do a small bit of rewording. Although never in the Mass, in a few other places I have chosen to use "these or similar words". My choice, however, of "similar words" is to use words that are more technical and reverent than modern English tends to be.
Therefore, while some wish to take advantage of the allowance for "other words" and make the ceremonies more casual and relaxed, I choose instead to take advantage of it and do what I can to make it more reverent. Generally speaking, the Mass (even the Roman Missal) can be done quite reverently if one just follows the exact words and rubrics that are laid down and avoids anything off the cuff. The tendency of priests and bishops who are more modernist in their perspective to aim at making the Mass more of an informal and "everyday" event has been bearing fruit for a half a century; and a careful examination of the fruit shows that it is rotten (rancid, in fact), and we know what Jesus said about rotten fruit.
In truth, there are only a couple places that the Church allows for improvisation in the Mass (and they are not in the Eucharistic Prayer). So, I cannot possibly tell you just how much improvisation would make a Mass invalid, but why would you want to play on the edge of a cliff? Stay away from it. When people feel casual in the Mass, they may keep coming back, but it is not because they experienced the presence of Jesus. It is rather, because they were either entertained, or they felt good about themselves (or both). When people feel reverence in the Mass it will impact them. If they are impenitent, they will leave because they feel uncomfortable around Christ; if they are penitent they will keep coming back because they want to be with their Savior.
