The ability to add user-defined genres is crucial for my tagging process. I have a few other custom tags, that tend to get repetitive and was hoping for a feature that allows you to add user-defined lists to other tags so that they autocomplete in a similar way. Thank you.
None of the tag fields autocompletes.
Yes, you can add, display, modify and delete (and all other tag field related tasks) user-defined fields if the tag format allows it.
I think there is a misunderstanding
@abbeyroad34 is asking for a way to defined a list of fixed standard values that are then also available from the drop-down lists on the Tag Panel (similar to what custom genres provide). These values then auto-complete when typing in the respective field on the Tag Panel.
To answer the question: it's not possible at the moment. A workaround is to use a set of actions "Format value" for the fields in question. You can then apply this action whenever needed. You can group them in sub-menus by using the # character in the action-group name which serves as a sub-menu delimiter.