too much voltage after adding headlight relays

I'll make a guess... they gave you the wrong ballast and its resistance is higher (too high), thus it draws less current so the total current draw on the blue wire lower. This would make the voltage drop wherever it is occuring less and so you are seeing more voltage to the VR and it is trying less hard to boost the voltage to compensate. So, yes, hold on to the old ballast.

Check the voltage while running in the following order; the voltage will would normally very slightly at each point but it will drop at one of those points a lot and you will know it is back upstream from there. Keep the - lead of the voltmeter to the same ground point at all these readings.
1. Large lug at the starter relay
2. After the fusible link to the bulkhead connector (connection J)
3. At the red wire in the harness connection to the ignition switch under the steering column
4. At the dark blue wire in the harness connection to the ignition switch under the steering column
5. At Pin N of the same bulkhead connector as in 2 on the dark blue wire
6. At any point you can access in the dark blue wiring to the VR

Why? The connections in these cars get old and corroded and wires get hard and can crack. You probably disturbed something that was on the edge of being bad. Don't worry at this point; troubleshoot as above. When you find the problem, the 'why' may become obvious.