Yes, a wire brush by hand will work fine without damaging the tag.
When I compare the B51 and the C55 to the Y0 code it looks like the y0 code is actually a Y05 code. That is the build to USA spec and most tags have this on them. You will notice the cuda tag also has the Y05 build to USA spec.
Y02 is a radio edit waiver of which I can't say I have ever seen on a tag. I'm sure it is out there somewhere on a C body cop car.
That's awesome your challenger is a D21 4 speed car and FK5 is definitely one of the best colors on a challenger. Really like the C55 without having the C16 added on.
Also, the N41 without N42 is pretty cool also. A very sleeper style car.
Cool car!! I hope you get to putting it back together.