Changing currency on a project contract linked to in progress project

Hi all;

I have a project that has been setup and has been running on an incorrect currency. The customer account for the project contract has been set in Euros and not GDP. I know I can just go in and change the value on the project contract to GDP and open transactions will switch to the new currency as will the contract value. My question is how will projects do any retrospective changes to any posted transactions and invoicing to reflect the new currency? How can I track those changes?

AX2012 R3.

Thanks;

Nigel.