Even sankhara and vinnanana does not evolve according to one’s wishes! Then if we say that we have the “free will” in some aspects, does that not mean there we are seeing some things as “atta” nature, to our control? Is it not the same as saying ” Let my sankhara be the way I like; let it not be the way I don’t like.” Will there be any exceptions? The verse said that it is true for saṅkhārakkhandha, or any sankhara that will ever exist! If we say that we have a small amount of free will, then it also means that there is a small amount of sankhara that we can control.
The statement regarding these aggregates not being under one’s complete control are made in the context of the rebirth process. When the kammic energy for human bhava ends, the next existence is not determined according to one’s wish but according to Paticca Samuppada process. One may wish “may I not be reborn as an animal or a hell being or a peta”, but if the kammic seed suitable for an apaya bhava ripens at the cuti patisandhi moment, there is nothing one can do at that point. Thus, the 5 aggregates evolve according to natural causes and not according to one’s desires in this regard. But after comprehending Buddha’s teachings, one does have control over the 5 aggregates, not in the sense that you can have eternal life in the heavens but you can gradually and eventually stop them from arising.