Hey, I’d like to help here with some clarification: the vulnerability affected winrar, not the RAR archive format. In fact, it happened when opening zip files, not rar files.
7zip is not only capable of extracting 7z archives, but also zip and rar. Thus using 7zip to open a malicious archive would prevent you from being a victim of said attack, which is what the previous author meant.
So you wouldn’t need to change the archive format of your existing files, as this was only about not using winrar to open possibly malicious archives.