My friend brought up an interesting point the other day and we have been unable to solve it.

When the third deck of the westeros phase comes up sometimes it gives restrictions to the planning phase; no defense orders, no march +1 etc. Would the player with the raven be able to change one of their orders to one of the restricted ones seeing as it's not in the planning phase?

No because the planning phase is not over yet:

"The player holding the Messenger Raven token may perform one of the
following actions at the end of every Assign Orders step of the Planning phase:

Replace an Order Token: The holder may swap one of his Order tokens
on the game board for one of his unused Order tokens."

Page 13 of the Rules also clearly has "Use Messenger Raven" as part 3 of the Planning Phase, followed by:

"After resolving this step, the Planning Phase is now over, and play proceeds to the Action Phase."

Cheers. That was really bugging me all week!

I want to know!!