Hi,
The action you tried would work if only you had already the main product price entered in the variant's price.
You'll have to run a MySQL query directly in your PHPMyAdmin to do that.
Something like that would add the variant price based on the main product price:
INSERT into #__hikashop_price (price_product_id, price_value, price_currency_id, price_min_quantity) SELECT main.product_id, main_price.price_value+2, main_price.price_currency_id, main_price.price_min_quantity FROM #__hikashop_product AS main LEFT JOIN #__hikashop_product as variant on main.product_id = variant.product_parent_id LEFT JOIN #__hikashop_variant as link ON variant.product_id = link.product_id LEFT JOIN #__hikashop_characteristic as characteristic_value ON characteristic_value.characteristic_id=link.characteristic_id LEFT JOIN #__hikashop_characteristic AS characteristic ON characteristic_value.characteristic_parent_id=characteristic.characteristic_id LEFT JOIN #__hikashop_price as main_price ON main.product_id = main_price.price_product_id
WHERE characteristic.characteristic_value = 'XXX' AND characteristic_value.characteristic_value = 'YYY'
where XXX is the name of the characteristic and YYY the value of the characteristic you want to target, and #__ the table prefix of your website tables.
As you can see, that's quite a complex MySQL query...