make "variant code" based on characteristic

Hi,

The code is already generated based on the characteristics. The ids that you see in the generated code correspond to the id of the characteristics values of the variant.
It's better than using the value name because you can change the value at any time and you won't loose the links between the variants and the value.
It also allows us to greatly improve the efficiency of the characteristics system as the SQL queries managing the variants can be optimized.
So no, you can't easily change the way the code is generated for the variants. You would have to modify the function updateCharacteristics of the file administrator/components/com_hikashop/classes/product.php which has almost 1000 lines of code optimized for an efficient generation of the variants, so it's going to be really complex, even for a senior programmer.