the quesion is not clear. If a mutation become fixed in a population, it is an evolutionary change indeed. Affect seems inapropriate in this sentence.

If a new mutation is neutral, that is, if it doesn’t cause a change in amino acid or it causes a substitution that has no effect on the function of the protein, then the population will not be immediately affected (but a subsequent mutation could, in combination with the first mutation, be of significance). If the mutation reduces fitness, then negative selection should remove it fairly quickly from the population, so the population remains unaffected. If the mutation increases fitness, then positive selection will increase its frequency in the population, to the benefit of the population over time. Sometimes, though, mutations that by themselves can reduce fitness occur in a gene that lies close to another gene that has an allele that increases fitness, so the "bad" mutation can hitch a ride with the "good" allele of the other gene and increase in frequency in the population, even though it is bad.