There is no rule that would cover this. I think, and this is just my opinion, that I would change the colons to braces or brackets and explain that change in a TN (as the colons are basically grouping text). However, since UEB is pretty big into the "follow" print concept, you wouldn't be wrong to do just that and follow print. I would, however, still explain the format to your reader in a TN on the TN page as this is a very unusual print format.
It amazes me that the publishers/authors still come up with new ways to present material all the time!