[Xervils]

I ended up editing the Python code itself to make it use Snaps by default instead of Boxfronts...

For newly created launchers:

disk_IO.py

'roms_default_icon' : 's_boxfront',

[REPLACE]
'roms_default_icon' : 's_snap',

To fix existing launchers...

categories.xml

<roms_default_icon>s_boxfront</roms_default_icon>

[REPLACE]
<roms_default_icon>s_boxfront</roms_default_icon>

This had been driving me nuts since I started using AEL a few months ago and it's nice to finally get around it.