I can't remember if it was this forum or another one but someone described rebatching soap and adding milk instead of water (you only add a teeny bit of moisture when rebatching, like a tablespoon or two). I think it's "okay" to do and I've done it myself. (I actually despise rebatching but that's just me and I've only tried it with
one milk soap batch that wasn't the way I wanted it.)
Anyway, I haven't really noticed that's it's gone funny or anything (I just pulled it out of storage and smelled it right now ... ). Technically though you would think the addition of (non saponified) milk would be an issue but it doesn't appear to be. At least not yet. Hmm ... now I'm wondering about this!
PS: I've used both the "slush" method and just adding a little milk at trace and either way works great. Depends on how much milk you want in your soap (vs water) and how concerned you are with color/overheating/appearance/etc. I've got a couple of posts about my milk soap adventures on my blog if that helps
Karri