When you create a new Subtype, just remove the the inheritance of the parent type. So you won't need to do it the next time.
A simple solution is to change one subtype. Export the type wt.doc.WTDocument (all subtypes are exported too), compare the exported types (search for the example you've changed) and then import it again.
look for something like this:
<csvPropertyValue handler="com.ptc.core.lwc.server.TypeDefinitionLoader.processTypePropertyValue">
<csvname>instantiable</csvname>
<csvisDefault>false</csvisDefault>
<csvvalue>true</csvvalue>
</csvPropertyValue>
https://support.ptc.com/appserver/cs/view/solution.jsp?n=CS30168