I've tried using your code on my system but even `getValues()` will always only return me the first value in a multivalue text field. `setValues()` will only work if I pass a single value or an array with exactly one value; all other scenario's don't set any fields in the GUI.

Based on that I believe you would have to use the Anguilla framework to manipulate your field values; the previously mentioned [cookbook][1] has examples for field manipulations.


  [1]: https://github.com/TridionPractice/tridion-practice/wiki/AnguillaSnippets#get-or-set-the-values-of-a-field-through-fieldbuilder