In this particular case you can consider codons coding for the same amino acid as synonymous, restricting, as you mentioned, the possible mappings to the ~20 pr

In this particular case you can consider codons coding for the same amino acid as synonymous, restricting, as you mentioned, the possible mappings to the ~20 proteinogenic amino acids. Another possibility for expansion would be to take advantage of the genetic code’s degeneracy/redundancy and reprogram it to allow non-canonical amino acids in certain synonymous codons.