You can repack eXtensible Archives (.xar) to any other similar compressed archive format, including ZIP. The easiest way would be to use some program with support of both .xa and .zip file and simply repack them. Alternative would be to first extract .xar files with one tool and compress it to .zip with another tool.
Convert eXtensible ARchiver archive to WinZIP Compressed ZIP archive.
We have found one software suitable in our database for this conversion.
Microsoft Windows software - convert xar to zip on Windows
A free open source archive utility
Convert from xar file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.