Change LiveID primary email address

I requested this years ago, and whoever was the Live ID PM back then said they were "looking into it." It's incredibly annoying.

I have everything, everything I want on one Live ID. My XBox Gamertag, my MCP things, Channel 9, MSDN forums, e-mail, everything. Except messenger. Which means when I sign into WLM, the contacts are different than those in Messenger. Which means I always have to use two different Live ID's to sign in, and Windows always chooses the other one by default. I could tell all my contacts to add my account on the new Live ID, but that's a nightmare. I don't want to lose their message histories, and I don't want them to lose mine. People who are offline may not get the "Use this new account!" message. All sorts of stuff. The thing is that I don't want to change messenger accounts: I want to use a different Live ID to sign into it. That way I can finally ditch that old messenger email address and nobody on my contact list will know what happened. This isn't possible, and if past correspondence with the Live ID team is any indication, it won't be for years, if ever.

The thing is, for messenger at least, that's not even it. There's some alphanumeric number that's your messenger unique profile ID or something. There is (or was) some way to get it, but I'm not sure if it still works. I saved mine in OneNote, hoping that one day some Microsoft employee will say "Oh, tell me your Messenger unique profile ID, and I'll just change the sign in email address to your other Live ID's email address". It's like a dream I'm perpetually chasing.