Analytics has an option to add opt-in links as part of its opt-out functionality. (using query parameters with the opt-out service)Add an Opt-Out Link
Please add this feature to the Target opt-out link service. Adding an Opt-Out Link
There are many use cases for this and even more now that we are post GDPR. Also in this post GDPR world some vendors like TrustArc are incorrectly configured to disable ALL Target testing internet wide across all target users.
Here is a great video describing an issue this new feature could help fix.
In this case the vendor TrustArc opts users out of Target Internet wide. A feature like the one I describe able would help to undo a global optout like this.
GDPR bad practice from Weather Underground & TrustArc - YouTube