Mime settings are the file type recognition part of a web browser. Archive formats like .lha .zip .lzh and so on should be just saved to to the hard disk unconverted.
I would recommend you not use WinRAR to try to unpack the Amiga archives. Just download
LhA and run it from the shell in AmigaForever and it will unpack itself. Then you can unpack other .lha files using "lha x filename.lha drive:path/" where filename is the lha file you want to unpack and drive:path/ is the place you want to decompress the files to.