Hmm yeah, we just have the one user (myself) right now that creates both kinds of emails (MLM & MSI).
The reason for wanting a different footer is the sales insight emails are a bit more personal than most of our MLM emails (aside from nurturing emails, which I would also like to change the unsub footer for) so the text needs to be slightly different.
I've used other MA platforms that allow for this, so was curious how I would set that up in Marketo, but it sounds like it's not easily done.