Modding Help Best practice -patching files and sharing scripts vs. creating new ones?

When making a new asset, which is generally best practice in these circumstances:

• Patching JSON files vs. creating new ones when modifying existing assets?
  
• Creating new script and animation files when making a new asset, or reusing existing ones from an asset with similar behaviours (assuming the original script/animation contains more functions/states than the new asset will need)?

Is there any performance difference in each case, either on startup or in-game? My gut feeling is that in the former instance patching may have a tiny impact when loading the game, and in the latter case using fewer discrete scripts may have a tiny effect on in-game performance, but it'd be good to know for sure.