I’ve added more than 8 external IDs for a single profile many times using TN Console. This shouldn’t be an issue.
What you won’t be able to do, is add multiple external IDs for the required ID type. For example, if the required ID type is configured to be DUNS (the default) then each profile can have only one DUNS external ID.
#B2B-Integration#webMethods#Integration-Server-and-ESB