If USCIS wanted unopened transcripts only, they would have indicated it in the guidelines. A transcript is considered official and valid, only if sealed and closed, for education purposes. A lot, if not most, of the time they're only considered official if sent from one institution to another, which is obviously not the case with this process.

Remember we have to construct our evidence packets so that it's easy to access for the Immigration official reviewing our case. Why would you want him/her to lose time opening envelopes?

If you're still unsure, wait for more detailed guidelines to come out on the 15th, and/or call the hotline and ask them directly.