[morzh]

The field coil is often used as a part of the DC filter, and also as a way to drop the voltage to the needed value.
Changing it will affect the result of filtering and the voltages in the schematic.

While there is certainly some tolerance built into any tube radio circuitry, it is still a good idea to adhere to the initial specifications as much as possible.

The specification of the DC resistance are usually known: they are listed in the documentation and are often printed in the schematic.
The type of wire could be easily determined by gauging the wire from the old coil.
Then find out what specific resistance (Ohms per Foot) the wire of that gauge has.
Then see how many feet you need to achieve the target resistance.
Then using the same or the same type bobbin wind the calculated length of the wire onto that bobbin.
If done neatly, the resulting inductance and the magnetic properties (as well as the thickness of the winding) will automatically go pretty close to the original specifications.

I do not think you could easily damage the radio, but much lower resistance will result in the hightened B+ voltage and so in the tubes running hotter.