Prestashop prestashop 1.4.7.3 issus

Hello ////////////////////////////////////////////// /////////////////////////////////////////////// Hello, we have a little new modify to do on website. Prestashop actually give opportunity to select customer group as you know each customer group has if you want a discount but if we want to apply to a group an increase it doesn't work Our intention is to apply in the group an increse in % to some group we need a little modify to our prestashop 1.4.7.3 to make increment in percentable to customer group