Any question answered...

Give it a tickle with some sandpaper?

Good idea, shine it up after?

what kind of seat post is it? Modern/wintage? If you find someone with a lathe it's a super easy/fast job.

Shimano Deore seatpost, new old stock. I want to shove it in my Geoffrey Butler which I date to the mid 90's.

Just get an inverse shim.

Hen's teeth Oliver. I wrapped a power band around the seat tube, fingers crossed the hologram hasn't run out.

place bike in 32c sun.
place post in freezer.
wait.
grease.
insert.
hope frame doesn't explode.
never need to change saddle, pedalss, or shoes.
accept devaluation of bike.

In seriousosity, might the seat tube split where the bolt is?
.2mm seems like nothing, maybe I'll sand it then put it in the microwave, then the fridge then grease it and ram it down the tube.