What I am assuming is your question is a part correct answer and part incorrect. Although yes most of the time if one were to substitute one amino acid for a different one we can end up with something that doesn't belong which can disrupt the the molecular composition of the protein we are trying to fold which would lead to a misfolded and defective protein. However, sometimes an amino acid is switched out with another amino acid that contains very similar properties as an amino acid as a whole and functionality of the R-group is similar thus resulting still in a "normal" functionally active protein that isn't shown to be effective by much.
