During a campaign game, you can modify the ship(s) assigned and crew quality by the edit command for the file \aos\00000x.cpg x= campaign #1, 2, 3 ,4 ,5 etc..... Ships are listed by line number in the main.oob file this is listing #1 in the columns format of 00000x.cpg. Just goto main.oob and select the ship you want! The second to last series of numbers in the column is crew rating:

0=a (best)
1=b
2=c
3=d
4=e