Is there a way to have two keyboard shortcuts for the same function? I saw these instructions to replace a shortcut

On your Mac, choose Apple menu &gt; System Preferences, click Keyboard, then click Shortcuts. Select App Shortcuts on the left, click the Add button , click the Application pop-up menu, then choose a specific app or All Applications.

So I can add a shortcut named 'Copy' under all applications, and insert ctrl+C as the keystroke. But then cmd+C won't work as the Copy shortcut anymore.
Is there a way to have both?
The Shortcuts Prefs won't allow you to add the same Menu item twice, so no, this cannot be done.
Additionally, in Finder, the Copy menu item is a 'smart' structure, meaning it always contains the name or count of what would be copied by the key command. You cannot use the shortcut replacer at all on a smart menu.
Examples…

Furthermore, attempting to override a system-wide command like Copy is bound to fail somewhere. It's definitely best to stick to the system defaults for such as those.