I am running X9 with an XT front mech all 9 speed. XT cranks double with hope bash.

Looking to move to XT 10 speed. Have all the bits covered with the exception of the cranks/chainring. Can i just swap out my current chainrings for 10 speed equips using the granny and middle positions?

Your current rings should be fine as the internal width of a 10 spd chain is the same as a 9 spd

Yep. All my chainrings are marked as 9/10 speed

That is fantastic.

except that your current worn chainrings will cause your new 10spd chain to wear into the worn chainring, causing the new 10spd cassette to wear to the newly worn chain

I think thats a little over dramatic dont you think?
A worn chainring is not likely to prematurely wear your chain but a worn chain on a new ring will prematurely wear the ring. If the rings are in reasonable condition there is no reason why they cant be used.