Bryan,

The sanding of a light cigarette burn ~~~ ahh that is a hard one, it's rather grey and I can see both sides of that issue. If it just needs to be cleaned OK but sanding 'altering' the surface. But you could argue so do abrasive cleaners. So that is a tough call.

Removal of a cancellation (I think) is very much an alteration. There is a large price/value difference between the two. Removing the cancellation dilutes the quantity of chips never cancelled and would skew the value for those who do have legitimate UN-cancelled chips. I don't see this issue as that grey as the other.

Back to you...