Unable to modify array from output of function

I have a function that takes an input of an enum, switches from that enum to return one of two string arrays. Outside of the function I cannot modify the returned array in any way, not via “get” “set array elem”, “set by ref”,“add” or “add unique”. There appears to be no way to modify the original, selected array outside of the function once it has been returned.

Is this intended? Am I missing something here? It doesn’t seem particularly useful to be able to return an array if it is strictly read-only.

Here is the switch function returning a string array:

Here is the function being called, and attempting to add to the returned array:

Here is in game, after adding text to the text box, and clicking the +LTRS button

And here is after the Print Letters button is pressed: