I just recently changed some T0 equipment to not have any mod slots.
Not sure if 8 will work (you might have to adjust the UI) but here is the code that you would need to change:
Look for this line in the items.xml file
<passive_effect name="ModSlots" operation="base_set" value="1,1,2,2,3,4" tier="1,2,3,4,5,6"/>
Tier is the quality level of the item, value is the number of slots available at that quality level