Did you try the Remove method I described? I found a great way to do this, you first select the components (in the Browser tree, forgot to mention that before) that you don't want imported into another assembly, right click and choose Remove, as I described. Then in the timeline, select all those remove/delete features, right click and choose Create Group. Then, you can select the group in the timeline, right click and choose Suppress features, which will bring all those components right back! So it's just a one click deal of unsuppressing and suppressing the group to remove and bring back the components you don't want imported into other assemblies! (simply being mindful of the unsuppressed/suppressed state of this group when saving the assembly to be imported elsewhere)
I found you can also create a selection set of selected components in the Browser tree, but with this great grouping and suppressing/unsuppressing ability in the timeline, selection sets for this appear unnecessary.
Will be interesting to hear how this works for you!
Jesse