A question for JAXBA, hoping you don't mind my asking

When you voluntarily re-route a Oneworld Explorer itinerary, am I correct that the following occurs:

• You receive back what you have paid in taxes and (sur)charges on segments you are dropping
• You must pay the taxes and (sur)charges on the new segments you are inserting
• You must pay the USD125 re-route fee

And so what you pay is the net of the above three items (which of course, in theory at least, could be a refund)

I ask because I am just about to re-route the last six segments of my DONE5 and want to be forearmed on what it is likely to cost me (by running the numbers in itasoftware)

Also, do you happen to know if BA collects surcharges (meaning YQ and YR) on RJ and QR segments?