I have a DigitalAsset with a box sop inside a geo node. When it is converted to staticmesh in FHoudiniEngineUtils::CreateStaticMeshesFromHoudiniAsset the vertexCount inside HAPI_PartInfo is 36 instead of 24. I assume that there is some point where Houdini API is configurated to triangulate geometry on cooking process.

Can I avoid this behaviour?

Currently no, as HAPI / Houdini Engine has to refine geometry before sending it the host application/plugins.

We do have some plan in the future to improve on that, as well as adding better vertex welding and geometry conversion on the HAPI side.