Do all dna sequence mutations result in down-stream amino acid changes?

No not necessarily, there are several different type mutations, there are frame-shift mutations and substitution. Frame-shift is when one is letter is missing or added to a codon, completely changing all of the amino acids following the mutated codon. When dealing with silent substitution, it is still a mutation but it is called silent substitution because even though one of the letters in codon changes, the amino acid will remain the same. Missense substitution will only change that one amino acid and the rest on the amino acids following will remain the same.