Change comma separated list to :: separated list

Hi All,
I created a custom embedded data field and I want to remove the commas (,) from the separations. I would prefer to update to say "replace , with ::" but I am also amendable to removing the , altogether and programming :: at the end of each question selection.
Here is what I have so far:

This is a multi-select question, and I need to display in a list like this inpatient::board, etc.