[Help] Editing existing sheets.

I've been thinking about running a game that is heavy on house rules, and I was wondering how I can edit existing sheets rather than starting from scratch.  For instance I'm thinking of using 2d10 instead of d20.  In theory this seems like a simple change, but I can't figure out how to actually get access to the code of a sheet so I can edit it.  Any help is much appreciated.

Which sheet are you wanting to modify? The code is available on  Github , so all you'd need to do is download the html and CSS files and modify the things that need to be modified. I do my editing in a regular old Text Editor (albeit, one with syntax highlighting for HTML and CSS), but you can also do directly in roll20.

I'm looking to edit the base D&D sheet and the sheet for The Void.  This should be really helpful.  Thanks.

Aaron, it's definitely easy to do and can turn out nicely. I have edited the 5e sheet to include a new tab entitled 'House Rules' and also include a madness counter, madness type text box, deity, faction, etc. on the front sheet.  If you need any help let me know.