Sorry, I remembered incorrectly, I though there is a difference between AC20 and AC21 in this regard because there were some big changes in the organization of the IFC Translators Dialog in AC21.
So, the fact is that IFC Properties are not available as criteria in the Override Rules Dialog so you cannot override elements based on their IFC Properties. I think this was a conscious decision on the part of GRAPHISOFT because they introduced element Properties in AC20, so users should create custom element Properties instead of custom IFC Properties- the way it was done in versions prior to AC20.
As far as conversion of IFC Properties to element Properties is concerned, this is not possible at the moment during IFC Import. Interestingly, such Property Mapping is available for IFC Export so in the IFC Translators Dialog you can specify which ARCHICAD element Property should be converted to which IFC Property during IFC Export.
What you would need is a corresponding functionality during IFC IMPORT. Unfortunately, this is currently not available. Hopefully GRAPHISOFT will implement it in a future version. I do not see a technological reason why it could not be implemented (as it is already available for IFC Export), so let us hope it will happen soon as I agree it would be an important addition to the IFC Exchange feature set.
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