Cutting the wire, while effective, is not the best practice. Use of a thin flat blade screwdriver to winkle the red wire connector out of its receptacle, then taping it back to the cable with insulating tape in a tidy manner is the preferred option. You can always put it back where it came from later should the need arise.
If you really feel the need to selectively switch the motors out, as Colin said, use a separate supply, either 4 AA cells, or a separate BEC off the main battery, and disconnect all of the red wires.
Different manufacturers will source their components from different places, because of that there will never be a guarantee that a perfect match will ever be achieved universally. This is true in industry, equally so in models. There have been many cases of people getting lucky ignoring warnings in red ink, but it is not good practice.