Were you signed up on the mailing list? I don’t see anything about that on it…
As for your question no, it can’t manipulate the To header. When creating the SIP dialog the same URI is used for both the request header and the To URI. As for adding a “toheaderfield” to the channel structure this would not be accepted. Channel variables already exist that are generic which can be set and read. That would be the quickest way to do it.