replacing ipfw rule

[rihad]

Any way to atomically replace an ipfw rule?

i.e. do away without delete:
ipfw add 100 pipe 1 ip from aaa to bbb
ipfw delete 100
ipfw add 100 pipe 2 ip from aaa to bbb

This results in 2 rules being added:
ipfw add 100 pipe 1 ip from aaa to bbb
ipfw add 100 pipe 2 ip from aaa to bbb

BTW what happens when a pipe is deleted? Is the data queued but not yet 
sent lost or is it still sent?

Thanks.