If you don't care if there is more than one file with such a "middle extension" and want to run the risk of losing the others, this simple trick does it:

perl -wle 'for ( <1bn9.*.cnt> ) { qx(mv $_ 1bn9.cnt) }'

On the safe side, run it only once:

perl -wle '$_ = <1bn9.*.cnt>; qx(mv $_ 1bn9.cnt) if $_'

Cheers, Sören