Copy and paste comment on the adjacent cells

Hi all gentlemen.

A sheet, compose of groups of 9 items and their corresponding qty.
I need to have the same serial no. be commented on each items of the same group.
I am doing in this mechanical way:
1. add comment of serial no. on the first item of group,
2. copy and paste, with paste special>>comments, on the remaining items of the same group,
3. Repeat this sequences on the other groups, which means hundreds.

Other than these tedious procedures, is there any better way?

Many thanks