Originally Posted by Doge

You know the disclaimers.

I prefer to drill carbon fibre way more than anything else.
Reason is many/most times it is made with some bladder and the wall thickness varies anyway and it there is lots of extra material built into it. Then, even broken the stuff is tough. An alloy post/part will snap. Steel with bend and CF will crack. Of course enough force and it will snap too, but materials are different and the tolerances are different.
An Extralite (brand) part will hardly ever be modified. It is already perfect. A CF bar I have no issues drilling, but I understand where the stress points are.

Anyway - your bike is on a trainer. Drill. If you do not know where it is safe to drill, don't. But I think you are fine. Alloy will have tighter tolerances and you do want to be careful.

For example - for a cable - I'd drill in the side toward the middle of the head tube. Not a lot is going on there. If the welds are huge, maybe a weld. If they are finely filed -not a weld. If in the TT...careful. A butted tube in the butt/thicker section farther from the weld would be preferred over the thin area. Since alloy is typically not butted, an inc from the weld is good.
You might feel this with the fork / seat post out.