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You can modify a model from Drafting using the dimensions on the face of the dwg, but it's not using the 2D Synchronous modeling. Check out the Help docs under Drafting -> Annotations -> Automated annotations in Drafting -> Feature Parameters -> Inherit Feature Parameters and Inherit Sketch dimensions.
For Inherit Sketch dimensions, you are basically showing your Sketch dims on the face of the dwg and modifying the Sketch from the dwg.
Tim Flater
NX Designer
NX 8.0.3.4
Win7 Pro x64 SP1
Intel Xeon 2.53 GHz 6GB RAM
NVIDIA Quadro 4000 2GB