Per Blog customizable Welcome / Notification / Password recovery emails

Hi,

I've been scouring for a while so perhaps this will turn into a RFP if no one has any suggestions.
Basically I'm looking for a plugin that would allow us to configure the text of many of the emails that are sent out based on what site they are on (or what site they are requesting the new password from, what site they are being added to, what site their account is originally created for etc)

I can't seem to find anything remotely close to this. Is this just an edge case? We have multiple departments or brands under the same roof, they need to share login info and be tightly intergrated but need to have different text and different graphics and the like.

I'm assuming this is all somewhat possible with the incredible amount of filters I find almost everywhere, for all the email notifications and therefore would of thought something like this exists. Maybe my search terms are off.

Thank you in advance for any advice you could give on finding something like this, in modifying something that exists to match my use or in creating this from scratch.

-S