How do I update an XML attribute from an MSBuild script?

Question

I am using MSBuild and MSBuild Community Tasks (using XMLUpdate and XMLMassUpdate) to update various sections of my Web.config one thing has me stumped though. If I have:

Answer 1

To complete the answer given by keeperofthesoul (I think you should give him the bounty btw) take a look at:

Here I'm using %24 to write out the special character $.