Ok… I may have misunderstood what you were trying to describe earlier. Normally 4-wire smoke detectors should be wired like this:
If you were talking about doing anything like this:
…then that is definitely going to fry your panel. But perhaps you were referring to something like this:
That won’t hurt your panel, but it also won’t work properly for a different reason that I explained Reversing polarity on a 2-wire smoke detector]here. Basically, you cannot short the supply voltage for the smoke detectors and still have them be powered.
Now theoretically you should be able to simulate a 2-wire detector by doing something like this:
Here you have a resistor in series with the output contacts of the 4-wire detector. I’m not sure exactly what the value of the resistor should be. You would have to so some calculations based on the alarm current of a standard 2-wire smoke detector. I has to be a high enough resistance that you do not bring the voltage to zero, but low enough that the panel senses the change in current and goes into alarm.