Keep copy-pasting it into the new scenario files. As far as I know, even the ISS isn't there if it isn't in the scenario file.
You may also want to convert the RPOS and RVEL system into ELEMENTS, I'm not sure how to do this, but I do know what they do:
The RPOS and RVEL system tells Orbiter the exact location, heading, bank, velocity and what-not of a vessel. So, if you copy and paste a DGIV flying through the atmosphere (dosen't have to be the atmosphere, could be in space, on the ground, ect) into a scenario file, no matter the MJD of the scenario, the DGIV will always be in the same place, heading in the same direction.
Now, the ELEMENTS system, that's different. What the ELEMENTS do is tell Orbiter the "orital data", if you will, so the scenario's MJD is a direct influence on the loaded vessels position. For example, if you paste in the ISS using the ELEMENTS system, it will be in it's 'real' position, ie while loading the scenario, Orbiter calculates it's position according to the ELEMENTS.
Does any of that make any sense?