Can json files in games downloaded from Catalog be edited?

Sorry if I'm posting this in the wrong forum area.

This is a similar question to one I posted a while ago. But because there are now online leaderboards, I feel that it has new pertinence.

Games that are sideloaded as a .pdx file/folder can have their .json files edited, which would allow for "cheating" in a game, if the game stores its level layouts etc. as .json files.

This would be a problem for games with online leaderboards.

But I'm wondering if this is really a concern, because....

Only games downloaded from Catalog can have online leaderboards, and I am imagining that it's not possible to edit any files in a game downloaded from Catalog.
(Because, I imagine, it is not possible to copy the downloaded game to a computer and then back again.)

Is that true?