API Modding and Character Sheets

Just getting into modding roll20 and had a beginner question about its capabilities. I'm looking to edit the Cyberpunk RED character sheet and include some features I think are lacking or that would make aspects of my game easier for my players like new fields to influence attack rolls, include features that automatically add mods to skills and stats, and expand the weapon types and range tables. How feasible would it be to modify this sheet template directly? Is it something that the API modifications can do or is this outside the scope of what this can do?

Depending on which cyberpunk red sheet you are using, you can find the sheet code in the r20 character sheet repo on GitHub. Since you mentioned adding new attributes and behaviors, that's something you'll want to do in the sheet code itself (using it as a custom sheet instead of the one available from the drop down). The API (aka mod scripts) can react to data changes and cause data chani, but it can't affect the actual html/is of the character sheet.

So, it would be easier to copy the template I'm using and treat it as a custom character sheet? Do you know if there are similar mods out there that do something similar to what I'm describing? Not specifically for Cyberpunk RED but really any sheet for any system. 

Everything you've described is sheet code affected, not API script affected. It might be possible to make an API script that allowed you to do what you want without editing the sheet, but it would be very kludgy and likely not a great user experience. On the other hand everything you've described is a pretty basic html/js edit of the sheet code, with maybe some light css labeled on top.