I was thinking about a carbon seatpost for my Colnago Master Lite steel bike. Would it clamp in okay. Would it get scarred bad if I have to adjust it?
If they did a good job prepping that frame the seat tube should be nice and smooth inside. But, even if it is, I would worry about your clamp. The Master probably has a regular binder bolt, and a brazed-on seatpost clamp on the back of the tube. The risk is that when you tighten this it constricts on the carbon post which might drive the edges of the tube into the seatpost and that's going to damage or break a carbon seatpost. Ideally, you'd use a clamp that constricts without creating any pressure points at any spot on the post but that spreads the clamping entirely around the post. Carbon seatpost are super strong but if you put pressure on them in one spot you can break them just like stepping on a piece of bamboo. They just crack.
It'll take a little inspection and analysis to determine if you can go carbon, but my hunch is that it's not a good idea because that frame probably has an old-style binder that essentially puts all the pressure in one spot on the post. Of course, if Colnago modified the frame with a slip-on modern seatpost clamp you'll be fine, but I don't believe that's the case,
Thanks for the email and sorry if this is bad news,