Can I whitelist the extension on multiple sites in Tableau?
Yes, you can! In order to do so, you must have the settings enabled on each site. Note that you will only be able to do this if you're an admin.
1. First click on settings
2. Click on Extensions
3. Ensure that "enable users to run extensions on this site is checked" and that the same extensions URLs are added. This was completed for one site during installation and the settings should match for the other sites in order to be enabled.