Yes I have the parts and the instructions to do this if you need them , the 550 meter has 2 different version of the meter and you have to look at which value is in the meter than it will tell you which resister to use. The kits I made up has both the resister to use the one you need and the extra one can be tossed. There is 2 different resistors that have to be taken out and and replaced plus the correct pot that too has to come out and replaced. The thing is you should know how to solder it in or someone that can as you you have to use a low watt solder pencil and the correct solder so you dont damage the circuit board. One other thing is you have to leave it apart while setting the coarse calibration inside the meter while it is hooked up, lot of people I notice dont get it set and put it together only to see they cant get it to calibrate. It is all in the instruction I was able to copy off the Sovereign forum.
One thing to mention is the 4 screws in the face of the meter has to come out to get it apart, but the decal covers it so instead of trying to pull it off and put it back on when done as it dont stick on too good. I just cut little hole in the face plate where the screw are and leave it that way or when you know it works as it should you could put a small dab of black silicon on the holes, I left the ones I did open.
Myself I learned my Sovereign with the 180 meter and tried the 550 on some I took on trade and switched all to 180 before I sold them as they were easier to understand on the close tones.
I take it from what I have read that 550 meter you got does work correctly as I though some of the XS2 meter didnt work on the GT.
Rick