if its Celtic and Rangers you want to swap
make a edt file and put this in it
"SWAP_TEAMS" "1569" "737"
"SWAP_TEAMS" "1570" "734"
& make a ddt file and put this in it
"RETAIN_PLAYERS" "1569"
"RETAIN_PLAYERS" "1570"
put both files in C

Program Files\Sports Interactive\Football Manager 2006\data\db
and run a new game