Go でマップ内のスライス値を変更するにはどうすればよいですか?

<code class="go">var aminoAcidsToCodons map[rune][]string
for codon, aminoAcid := range utils.CodonsToAminoAcid {
    mappedAminoAcid := aminoAcidsToCodons[aminoAcid] // Return slice by value

    if ok := len(mappedAminoAcid) > 0; ok { // Check if slice is nil
        mappedAminoAcid = append(mappedAminoAcid, codon) // Create a new slice
        aminoAcidsToCodons[aminoAcid] = mappedAminoAcid // Reset map value
    } else {
        aminoAcidsToCodons[aminoAcid] = []string{codon}
    }
}</code>

<code class="go">mappedAminoAcid, ok := aminoAcidsToCodons[aminoAcid]
if ok {
    mappedAminoAcid = append(mappedAminoAcid, codon) // Intended but incorrect
}</code>

<code class="go">var x map[string]string
x["a"] = "foo"

y := x["a"] // Copy string by value
y = "bar"

// x["a"] is still "foo" since a new string is created in y</code>

<code class="go">aminoAcidsToCodons[aminoAcid] = append(aminoAcidsToCodons[aminoAcid], codon)</code>