Can't move the cf seatpost in my aluminium cross frame- I suspect corrosion has occurred. Is there any way to confirm this is the case? Is there any way to remove the seatpost without too much damage? 😥

How did you grease it? Have you applied anything else to the bonded area since?

Can't remember, but I suspect Shimano grease, probably about this time last year. Seatpost hasn't been taken out or moved at least all summer.

not supposed to grease CF post unless you use specific 'carbon friendly' assembly paste.
ie: http://www.jejamescycles.co.uk/tacx-carbon-assembly-item105138.html
(other makes and suppliers are available)

Mine stuck in (at the right height admittedly), so I spent a couple of week soaking it with GT80, and rode it with the seat clamp undone, it eventually came free without any damage.

I remember something about CF absorbing the components of normal grease, thus swelling and jamming. And not the good Bob Marley sort, nor the WI type.

coca cola down the seatpost (with bike upside down)? CC is a dilute phosphoric acid solution which should dissolve oxidation.

Lots of warm/hot water around the joint, in the hope the frame will expand more than the CF post?