Help requested for REGEX

Hello,

I wonder if someone could write a Regex to help me: It is a quite simple one
(for someone who knows about Regex!)
I use to receive email containing the same sentence "Waiting for agreement"
I want by replying keeping the same text as in original message text BUT
replacing  "Waiting for agreement" for "Pending"

Could some one have time to spend on it ?

Thanks

Didier