I guess I misunderstood a little. When you said you were planning to ride the bike fixed with only a front brake, are you saying you DIDNT get a machined front rim for brake use? You're best to get a machined wall for brake use. It gives a perfectly flat surface for the brake pad.

The way you made it sound is you got one front machined, a non-machined rear and since you were thinking of riding SS some of the time, you were thinking of adding a rear brake and were worried about the rear wheel not being machined. If you are only riding SS some of the time, just keep a front brake with a front machined wheel. If youre worried about matching wheels, I guess return the both for 2 machined wheels? I guess we dont know what you currently have LOL. 2 non-machined wheels? 1 machined front and NM rear?