As i remember Metin2 uses the Navicat Datasbase for storing account data. In Databases you have the option to cut those which are longer than the possible Charnum to the maximum of the other Database or you can set the Charnum higher. I dont know if it is usefull or have any other effects to the server to set the charnum for characters higher.
But if there will be a possibility for every character to change its name it would be simple to cut the names which are at the limit and then add Sg2 at the end. I think After you cut the names you dont need to add the initical of sg2.