I did that today with no primitive ID conflicts, but I copied the associated MOp separately, THEN generated a new primitives ID list after the copies were complete. When I copied the MOp, it did create some id conflicts. They didn't matter, because I repaired the MOp's primitives list afterwards.
The list from an old 9.8 drawing ALSO DID have duplicate iDs with my already-populated 1.0 model into which I was importing the primitives, but CB automatically reassigned them new IDs as they were copied. Since I copied them into their own layer, it was easy to correct the MOp, simply by selecting the MOp's primitives list (three little dots), then selecting every primitive in that new layer I'd created.
Selecting even a LONG list of primitives is easy. Click on the first one in the layer. Cursor to the last one and shift-click. Those two and every one between will all be selected. Then just hit ENTER. That REPLACES every primitive in the MOp, it doesn't just add them, so it instantly does what you want.
Bingo! The MOp is corrected.
Lloyd