My opinion: Yes, you are right. Never touch a running system. But if there are problems with certain codecs, it is the recommendation of the user community to install the codec pack. Every program that you install, which is not maintained by the manufacturer of the OS does interfere with the OS. Have a look at the magix forum. If there are problems, the always recommenadtion is: "make a clean install of your OS and install the magix product as the only software". They recommend that because of the missing interference between other programs, the OS and magix. I think, CL would recommend the same.
The codec pack interferes, yes, but as far as I know, it solved problems with some special footage from exotic cameras. So if you don't have problems, don't install it. But if your footage cannot be played or is not recognized, the codec pack can help.
I have the codec pack installed, and my PD runs absolutely rock solid. That is the reason why I changed from magix.
Hatti
Win 10 64, i7-4790k, 32GB Ram, 256 GB SSD, SATA 2TB, SATA 4TB, NVidia GTX1080 8GB, LG 34" 4K Wide, AOC 24" 1080