Question:

If a decision is made to make a field multi-select, can this be changed back to single select in the future?

Answer:

No.  Once a single select field has been made multi-select, this can not be changed back, even on the back end.  This would cause large issues with the field being properly populated, when various documents may have invalid data.

This is a one-way switch, and cannot be changed under any circumstances.

Related Documentation:

N/A  

Thank you