Change products prices after 10kg are reached

[dario3004]

Hello people!
I would like to add a price rule in my shop so that after 10kg (only of 2 combined product, not 10kg of every product of the shop) all the prices in my shop are discounted.

I tried in Back Office cart-rules and price rules but can't find anything that let me define a rule like this. I can even code the rule, but I don't know which file should I edit:-\

any information about doing this would be great!! thanks everybody!!