How can I adjust the total cart price in liquid coding?

Hi, I am coding system that automaticaly applies discount for customers outside of my country . I have users tagged with specific tag, and I updated price.liquid so that price changes if user has that choosen tag. But when user enters cart prices are back to normal, same for checkout. I lookup and I found out that cart has object called cart that holds info about users current cart. And it that object there is final price. But I am not able to change final price. Is there a way to change something in that object ? Is threre way to change total cart price so hat when user checkout that price is used ? Can this be done in .liquid ? I need total price to be divided by 1.2

Thanks for any answers I am desprate at this point I tried everything using my .liquid knowlage