I've dyed a fair bit of LW nylon, although not the 20d momentum specifically.
I had good success with dying 1.1oz Olive Green 2nds that Scott at BWDD sells using regular dyes. I had great success using "Lanaset" dyes, which are really ideal for nylon.
The DWR on the 1.1 seems pretty on par with the "Momentum", but the "Momentum" has a much tighter weave, which may make it harder to get the dye bath to absorb into the fabric.
The trick with that is in the bath temp (I've successfully put the 1.1 into boiling water without any distortion, but I wouldn't go that hot, and definitely test water temps with a scrap.
The lanaset dyes are in a completely different league than the multi-part dyes you get for nylon/poly in the stores, and you can get alot of dye for around $10. I had problems with consistency and color fastness with the regular acid component dyes, and it would bleed when washed in warm water, lanaset/sabraset didn't have that problem.
I have no idea what the impact on the effectiveness of the DWR is, so dye at your own risk.
Here's a link with some info on the process: http://www.prochemical.com/directions/Sabraset_Immersion.htm