Hit open, select your file, go to tools, depth chart editor,, find your team, scroll to "KR", find your player in the list of players, select, press transfer, hit apply, close out, go to file- save, then exit when finished.
To have the QB as a KR you actually need to edit the DB_TEMPLATES.dat file. I believe it is within one of the tables of file #4 of the DB_TEMPLATES.dat file.
#1...make a copy of the .dat file. Put the copy in the My Documents/Madden NFL 08/ folder. #2...open the .dat file using the DAT File Replacer. #3...extract file #4 #4...open file #4 using the DB Editor. #5...locate the corresponding table and extract to csv #6...make the necesary changes to the csv file. #7...import the csv file into file #4 using the DB Editor #8...import file #4 into the .dat using the DAT File Replacer
That's the quick form of the instructions. Unfortunately it's been quite a while since I've located any of that so I can't pin point you directly to it. Sorry I couldn't be more help.
if you do it with madden amp you don't have to edit the DB, but if you want to make the changes in game, then you have to do the dat editor. IF you get it done through madden amp, don't load up the depth chart in Madden or it'll mess it up.