We would like to know if it is possible to configure the BOM to show only the components or to show only the first level's parts and subassemblies or a combination of them?
(But not in the drawing)
For example, in SolidWorks they have show, hide and promote.
Don't know about how it works in SW; Under the Properties for the Parts List within the List Control tab are options that are close to what you have described, though the 'Not in the Drawing' part is not clear to me.
Hope you find this useful.
Maybe what you are looking for:
Right click on the assembly tree, you can open Occurrence Properties. In here, you can turn off what is seen on prints, or in your BOM report, lots of stuff in there to change settings. You can also turn off what is shown on your draft, by right clicking properties of your BOM table.
You can control the parts list on a drawing by assembly configurations. This can be very powerful when coupled with the ability to unlink parts lists from one another. You can set the view display to one confguration and if you wish you can set the parts list to another to display whichever parts you want. To me, this is easier to manage than occurence properties or other means.
You can also display only items that are ballooned in the view.