Here is an example of what I came up with but I am not sure if my syntax is correct?
<append xpath="/entity_classes/entity_class[
contains((@name, 'zombie')
and not contains(@name, 'Radiated')
and not contains(@name, 'Feral'))
or contains((@name, 'zombie')
and not contains(@name, 'Feral'))
or contains((@name, 'zombie')
and not contains(@name, 'Radiated'))
]">
<effect_group>
<passive_effect name="DamageModifier" operation="perc_add" value="-1">
<requirement name="!HitLocation" body_parts="Head"/>
<requirement name="EntityTagCompare" target="other" tags="walker"/>
</passive_effect>
</effect_group>
</append>