Token rewriting means to rename a variable being sent through a redirect link. 

It's most commonly used when sending paid traffic from a traffic network to an affiliate network to a product you're promoting. The affiliate network may give you extra fields so you can save things like traffic sources or searched keywords from the traffic network, so you can learn which traffic sources and keywords resulted in sales. The problem is that each traffic network sends that information in different variables. Token rewriting fixes that, by renaming the variables during the redirect.

Usually token rewriting is pretty annoying. It means going in and editing links with special codes. We did it differently. In, you just manage the destination and tell it to rename any variables coming from traffic sources from the wrong variable name to the right variable name.

To demonstrate, I've setup this destination to display the variables that are sent to it and added it to (You would do this on your affiliate link destination instead.) 

To add variable rewriting, click on the "Variables" button on the management page for the destination:

That will bring you to this screen where you can configure variables for the destination. Pick "Rename a variable" from the first set of options:

And you will see this screen:

On the left, list off the variables you want to rename from the traffic sources, one per line. On the right, list off what to rename them to, again, one per line. There should be the same number of variables listed off on both sides:

In this example, there are redirect links coming from two paid traffic sources. One is sending the traffic source in the variable "ref", the other in the variable "trafficsource", but the affiliate network is expecting them to be in the variable "tsource". So, both ref and trafficsource will be renamed to tsource when the redirect happens.

And here's a redirect link for that destination with the variable "ref" attached. If you click it, you'll see that the variable gets renamed, and instead of it saying that "ref" = "hello", it says that "tsource" = "hello"

Once you have variables renamed, the status button will change on the management page for the destination: