I don't think you can create such a custom IFC type. That IFC Schema is a standard so I think being able to create custom IFC types would make it non-standard. Also, when exporting such an IFC file no other program could interpret your custom IFC type since it is not in the IFC standard.
All you can create is custom IFC Properties but you have to create them somewhere within the existing IFC Type hierarchy.
I think if you are delving deep into IFC, you should read everything there is about it in the ARCHICAD Help files:
http://helpcenter.graphisoft.com/guides/archicad-19-int-reference-guide/interoperability-2/file-hand...
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