At this time, alternative mouse housing options are not available for individual purchase. However, if you have a spare unit, you can swap the top shell with the housing from another Endgame Gear mouse within the same series:
XM housing:
XM1
XM1r
XM1 RGB
XM2 8k
XM2we
XM2w 4k
OP housing:
OP1
OP1 RGB
OP1 8k
OP1we
OP1w 4k