A MWC for a broken back box replacement? Surely not...!
I would issue what I felt was appropriate to the remedial works carried out. I would not be averse to using a cover letter to state Items x, y and z of the EICR dated blah have been fixed/remedied/sorted.
I often state that the cover letter and any new schedule of test results should be appended to the original report. BS7671 isn't clear on what to do in my view, but as long the end result makes sense I don't see a problem.
It depends on the nature of the issues found, and they can obviously be very varied.
I recently had multiple lost CPC issues on an install with around seven class I lights. Had to re-terminate four of the lights to get the CPC good again. My cover letter stated the work I did, the r1r2, the earth loop, and IR tests. I think that is sufficent personally.