I encountered this bug while loading:
"Duplicate XML node name bodyPartGroups in this XML block"
I rewrote the RatkinGlassesRecategorised.xml as bellow:

<?xml version="1.0" encoding="utf-8" ?>
<Patch>
<!-- Ratkin Glasses -->
<Operation Class="PatchOperationReplace">
<xpath>/Defs/ThingDef[defName="RK_ResearchGlasses"]/apparel/layers</xpath>
<value>
<layers>
<li>EyeCover</li>
</layers>
</value>
</Operation>
<Operation Class="PatchOperationReplace">
<xpath>/Defs/ThingDef[defName="RK_ResearchGlasses"]/apparel/bodyPartGroups</xpath>
<value>
<bodyPartGroups>
<li>Eyes</li>
</bodyPartGroups>
</value>
</Operation>
</Patch>

It seems work. I don't know if it's correct. Please tell me if you have any suggestion.