I guess you could put Matrix(n) folders on the SD/MMC, but HB units will only import from the MATRIX folder. You would have to manipulate those folders on your PC to set up importing the MATRIX you prefer.
I manage my Navdata in HumminbirdPC by lake. Each in its on .GPX file with data attached to I have a cycle of backup data. Ex: FORK_20130801x.gpx, FORK_20130815x.gpx, etc. x=a,b,c. . . if date is the same. Then upload from HBPC to SD/MMC for unit loading before on-the-water.