Is it possible to modify a 5 lead unipolar stepper motor to a bipolar?
When I read your post the fist time I missed the fact that you've already cut the traces.

From the photo it appears that Node 5 the common 5th wire is brown.  The first inductor pair are red-white wires, and the second are yellow-blue.  If you reconnect the trace you cut between red-white(around 10 o-clock on the photo) you will have a bipolar config.

I'm not an expert so I can't tell you if this would work, but it sure looks worth a try.