Is there an addon that literally divides the damage and heal numbers by ten?
 

If I for example, hit someone with a 100 000 crit, would it be possible to create an addon that just splits it by 10 and effectively makes it a 10 000 crit? Sorry if this is stupid and not achieveable in any way. Have a good day!

Where, specifically, is the number you're asking about displayed?

The damage numbers above units heads can't be changed. The number could be modified anywhere else in the interface, but it would be a pain to track it all down.