I just added:
<append xpath="/items/item[starts-with(@name, 'armor')]/effect_group[contains(@name, 'military without penalties')]">
<passive_effect name="ModSlots" operation="base_set" value="1,2,3,4,5,6" tier="1,2,3,4,5,6"/>
</append>
and the stealth boots work.
I cannot find the correct effect group for Chainsaws and Augers though. Impact Driver works fine - but chainsaw and auger must be tagged differently somewhere.
Any ideas?