It is certainly possible to repack RAR archives to DEB archives with many file archivers, but the resulting .deb file will most likely not be a valid Debian package for app installing, unless the RAR archive did contain files in proper structure for Debian, which means rar to deb conversion is somewhat odd.
Some Debian archives can be downloaded as RARs, which means they are double compressed. In this case you should just decompress the contents.Open RAR file Open DEB file
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