no, the icon you want is the one that is defaulted (regardless of DE/WM) that represents an archive... like .gz .tar and the like. Also, having it associated with archive programs that know how to handle it would be great as well... not sure if all of them currenlty handle .xz just yet... but the "archive icon" is what would be best used in this instance. It's technically a new filetype, so I can understand why it has no association as of yet. But that is the association that makes the most sense in the end.
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"Custom" is NOT mass produced... then it's just a product line.
Custom Processing Unlimited