You still get the MYP price that it was in affect when you ordered your MYLR. I can go into the edit-design page for my RN number and it tells me the price upfront before confirming a switch. Only difference for me is that $600 CAD increase in the delivery fees. Otherwise the MYP is the price it was on March 11th when I ordered MYLR.
I would have to pay $85,890 CAD for MYP with no upgrades. Current price is $91,990
Just use this link and you can edit your order and see the price upfront:
www.tesla.com/teslaaccount/edit-design/RN######## (use your unique RN# at the end).