Currently in modelbuilder you can Add fields (multiple), but you cannot Add Coded Values to Domains (multiple).  You have to add domain values one tool module at a time, which is time consuming.

Create an Add Coded Values to Domains (multiple) tool which allows the user to Paste In multiple formatted domain values, using a json dictionary.  This way the user can format the multiple values in excel and paste it into the tool, not type them into individual fields.