Using MS Release Management (v2015) we can use tags to deploy our applications to multiple servers sharing the same tag. This is useful for identical servers in a load-balanced environment. But how to do sever-specific actions using server tags, such as setting a website binding to the server's IP address?
As far as I can see there are no variables to be defined.
You don't. Tags are intended to run the exact same set of actions. If you have server-specific activities, you'll have to break those out into separate server containers.
I've done exactly that before, for exactly the same situation.