make own sheet in the current game (started with another sheet)

(I'm not native english speaker so sorry in advance if I'm not clear in my exposition) I'm playing my BECMI campaing (D&D red box) with BECMI sheet and I have a lot of characters in this sheet. As I'd like to have a personal sheet (also to have my house rule on it) and I'm totally unskilled about API and how make a new sheet my first question is: Can I, keeping the attributes of old sheet, trasform it in my new sheet without losing all characters, macros, etc I've already did? There is a way to move my game in a different sheet?  Thank you

You can do this.The attribute values aren't saved with the sheet - they are saved in a roll20 database. When making your new sheet, use the same attribute names as the old sheet. Your old characters will be fine. If you use a sheet which doesnt have the same attribute names, the old attribute values will still exist. They are still stored in roll20's database. So even if they aren't visible on a sheet, they still exist. If you then go back to the old sheet, or create a new sheet with those attribute names on them, the values will reappear.

Go to github and see if you can find the sheet code for the same sheet and modify from there. 

Thank you! Happy to hear (read) that. I've found the sheet, thank you, and learning the ropes for make my own sheet.