Yes, it is possible to create custom IFC Rules.
All IFC Rules are in the
"Graphisoft\IFC Rules 19.0.0 INT"
folder within your User Profile folder (such as "C:\Users\Joe").
They are XML files with a relatively easy-to-understand structure.
I think you can take an existing XML file, copy it and modify that. Make sure it is in this same folder because the Apply Predefined Rules Dialog looks for them in that folder.
Check the attached screenshot. Notice how the different fields within the dialog correspond to the different rows in the XML file.
Also notice how that hierarchical structure of the data entries are created by the XML file.
I think the <ApplicableTo> portions are important. For example, this XML code
<ApplicableTo>
<ClassName>IfcObject</ClassName>
<ClassName>IfcTypeObject</ClassName>
</ApplicableTo>
will make this Rule enabled in the Apply Predefined Rules Dialog, because you specified that this Rule set is applicable to IFC Objects.
There are other IFC Classes, like IFCStorey or IFCBuilding, IFCSpace, etc.
For example, the COBIE Rule set applies only to Zone elements. So if you select a placed Wall, go to its settings Dialog, then click Manager IFC Properties, click Apply Predefined Rule to get to this Dialog, then select the COBie Rule, you will see that its contents are grayed and you cannot apply a COBie Rule to a Wall. This is because the COBie XML specifies that it is applicable to IFCSpaces. So this is why the <ApplicableTo> segment is important.
From what I saw on the net this Masterformat is a classification system for objects, so the above should work, which is why you may want to make a copy of the CAWS XML and modify that copy.
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