Collagen is protein.
Every growing process in our body (after we put puberty behind) is about micro-injury. It’s what makes muscles grow in bodybuilding (which I am into).
Clearly the dick isn’t a muscle though.
But just like yoga over time impreoves dexterity via extension and therfore micro-injury to ligaments, PE can do the same. It’s clearly proven by the tribes that have ritualistic penile extension traditions. Given enough time, there is no doubt the human body can be shaped.