Here's a couple of thoughts:

1) Write Beth Shultis and perhaps even Richard Anderson and explain your situation, and ask them if you could help you by putting you on NW flights instead. Stress to them that you understand the logic behind your changes, and have no issues with it, and will certainly work with it in the future, but that you feel it's unfair to apply it to tickets already purchased. Perhaps they'll get you onto NW metal, or make an exception for the EQM.

2) If that doesn't work, after you fly, ask them again for the EQM.

I am sure their intentions were not to hurt their loyal customers (that hasn't been NW's theme for a while), and that asking for an exception is not wildly unreasonable.

Steve