Before you take apart the regulator -- take the regulator off and check to see if the coolant passages are clear. Put the regulator in boiling water and see if it does rise to 10mm.
But, before you do that -- so some more checks:
1. When the engine is warm does the eccentric screw bottom out? If it does not, it would indicate there is continuing fuel enrichment. Loosen the nut over the cone on the regulator to make sure the screw bottoms out when hot. This takes the fuel enrichment out. Do you still have the issue?
2. Again, when engine is warm, clamp off air hose that connects the warmup regulator to the bottom of the throttle body. This takes the warm up circuit out of play. Any change?
I think the regulator can be taken apart, but start with the above.
Byas