If your steel frame is a structural object, you should be able to suppress the subtractive 'feature' in the Building Element information panel, under the Features tab.
Having said that, this is another use case for more refined handling or filtering of AECOsim's perforaters.
It would be good to discuss what kind of filtering would be provided: Penetrations usually have something sitting within or passing through the penetration. Typical exmaples are doors, and beams or ducts. For doors and other elements provided by the AECOsim placement tools, I suppose that the developer codes what is cut and when. With the door example, the perforator is probably hard coded to run before the door object is inserted. I suppose that when the normal Mstn move command is used, the perforater is coded to always skip the contents of the cell being manipulated. The perforater also seems to skip anything encapsulated in a cell as well.
I suppose that this works OK for most simple door/window use cases. But, not if there are some complicated (or more 'realistic') requirements where say the opening in the window or door needs to be stepped or an additional material needs to be added to the wall.
I think that there needs to be some additional query tools provided in PCS, where a lot of these objects would be authored by the user. Recently, we were asked to notch the screed at the bottom of the steel windposts in the model to avoid reported clashes. I could see this being generated in PCS or using the new Parametric Solids; but there needs to be some 'if-then' type filtering to be really useful. For example, the perforater depths could be made to read the wall depth.I think that this is already coded into the Place WIndow/Door tool. It would be good to provide PCS the means to query the host object, and automatically set the feature to be suppressed.
Compound Cells can have multiple perforators; and there is some rudimentary control over the order of execution in the Building Information panel. You can also use the Subtract Solids or Cut Solids by Curve tools to manually generate the subtraction in the Wall, and then suppress the 'cut' feature in the object passing through the perforater's defined volume.