set a password on multiple existing rar files

I created a bunch of .rar files (hundreds of them), but absent-mindedly forgot to set a password (sigh). I could delete them and start the process again, but I'm afraid the deleted files would become vulnerable (with recovery software), so I would like to add a password to the existing archives, if feasible.

I have thought about putting each archive into a password-protected archive, but I'd rather have a single (non-nested) password-protected archive, if feasible.

The files are stored on exteal SD cards and HDDs and I have access to Linux, OSX, and Windows. I have a preference for a command-line solution, rather than pointy-clicky-draggy, and a strong preference for open-source and/or free software.

There is a Windows-based solution here: How to set password on already existing winrar archive and encrypt it also?, but it's not command-line so not really adapted to dealing with hundred of files.

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