So I was messing about with leaving and joining my tribe, when I discovered that I could click on and edit the tribe invite message. I'm not sure if it was a Steam Client specific thing, and I haven't tested on the regular standalone or on my browser, but I've only just noticed it.

Before:

After:

You can do this on any client/browser and you can change marriage invitations and also tribe.

Was not aware of other invites. Cool but weird bug.
e: Yep.. just tried it on the regular standalone and chrome. Works like a charm