yes, i think it was announced on the blog or some such - but it's rather manu-matic process, you upload the newest version to the channel#, the old version to another, private channel - then email us at partnerSuccess at roku.com to install the older version for older models.
i personally would suggest another approach - have a single version of the app and downgrade gracefully inside it. I.e. if it's low-end/legacy model, just don't show the new, fancy UI - go with the old one