Name the young character “YOUNG (Name)” and do @YOUNG NAME becomes @NAME
If you want to make the character have a young hairstyle (like pigtails or something) do @YOUNG NAME changes hair into (whatever hairstyle you want) and you can do it for all things like face shape etc
This makes the young version look like the customised MC and it doesn’t affect the actual MC’s looks at all as you’ve created a new one (YOUNG NAME)