I'm trying to create a Thai voice and I would like to change the positions of the consonants.

espeak-ng -vth "ภาษาไทย" --ipa gives me: pʰaː4sˈaːa2jtʰ where it needs to be pʰaː4sˈaːtʰa2j

To "reorder" phonetic pronunciation regarding to writing, you have to consider all characters in the rule, something like this:

.group a
    abc  cba

You may use pre) or (post rules before/after character group, if you want to choose depending on them, but don't want to jump to next group of characters yet. Also, if there is no canonical order for additional diacritic marks (like for Arabic vowels), you can make them in "canonical" order with .replace rule, e.g.:

.replace
    ca ac
    ā   ē

but currently you can replace only characters in groups, which together fit into 4 bytes (i.e. 2 ASCII letters to 2 ASCII letters, or 1 2-byte letter to 1 2-byte letter).