I don't change the bevel on Zwickeys. However, do need to take off the extra metal in the triple layer front part of the head so the file will lie flat on the existing blade bevel.
Also, many Zwickey Deltas, and I suspect the No Mercy's as well, have a concaveness in the blade. Put the blade edge on a file and look at it from the side. You will usually see light in a little arch between the blade and the file at the center of the blade. To get the blade straight along its entire length, I take some metal off the cutting edge of the triple thickness front. When that plane is straight, I follow the initial bevel of the blade its entire length with a file.
If you just start filing the entire length until everything is trued up, you will take off a lot more metal and usually reduce the width of the blade at the back. Good luck.