UPDATE - GOOD NEWS and BAD NEWS
So I just received email from Tesla that my change has been made - didn't ask for confirmation, just that it has been done now.
In reviewing my order, the GOOD NEWS is that my order now shows the white seats, and the total increase in cost was only the $1,500 (plus about $100 in additional taxes for the increased value).
The BAD NEWS is that it did reset my estimated delivery window from Sep-Nov 18 to Oct-Dec 18. That totally sucks! Moved back to the end of the line...
No more changes for me!!!
So if you requested Tesla change it, it appears that you will not pay for the price increased in the car or paint, but you will apparently restart your 2-4 weeks estimated delivery window. Therefore, if you do not want to wait the additional time, and are ok with the black seats, you may wish to forego your change request!