Yes, if using Origin 2016.
Say the matrix sheet is [MBook1]MSheet1, then
1) if the sheet is currently active:
wks.x.longname$="XLongName";
wks.y.longname$="YLongName";
2) by using range notation:
range rMS1 = [MBook1]MSheet1;
rMS1.x.longname$="XLongName";
rMS1.y.longname$="YLongName";
Not sure about Origin 2015.
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