Copying Built-in Chart Dashlets

Does anyone have any tips on making copies of or upgrade safe modifications to the built-in Outcome by Month and Pipeline by Sales Stage chart dashlets? I think the best approach may be to copy the existing code and make new, modified versions of these dashlets. It seems that simply copying the code to /custom/modules/Charts/Dashlets/[custom name] and renaming files/classes doesn’t quite do the trick. If I introduce new dashlets in /modules/Charts/Dashlets I’m thinking they won’t be upgrade safe.