Make changes to list of things depending on position in list

I got myself in kind of a problem, which is that I would like to make changes to everything in a sorted list, depending on their position in the said list. Is it possible (hopefully :crossed_fingers:) ? And, if yes, how can I do it.
Talking more practically, I want to add points to my user depending on their score, so, the first user earns, let’s say 100 points, I want the second to earn 99 points, etc.

Any help appreciated ! :grin: