1. Create a Custom User Field (guide)
2. Go to Amazon XML Mapping -> Universal Product Fields and map the RegisteredParameter field to the user field (guide)
3. The value that will go in for the items that need a UPC exemption are one of the following (depending on the exemption that you have)
- PrivateLabel (most common)
The rest of your listing should be setup as usual - as long as the value is submitted for registered Parameter.
Tip: You can set up a default value for custom user fields - so that every time the page loads, it will pre-fill with the value you select. To use this, you need to enter the value such as PrivateLabel in "Default:" when creating the field.