Almost every prerecorded interview would carry the disclaimer, rendering it meaningless. Though it would be fun to see "fake reaction" every time they splice in footage of the interviewer nodding, smiling, scowling, etc.

Almost every prerecorded interview presented as they currently are would carry the disclaimer. It might cause interviews to be presented differently (either ruthlessly trying to keep on topic, or with an easy link to the full interview), but even if not, having that disclaimer would be useful as an indicator that forced people to remember that what they are seeing might be out of context, and to look for that context.

Finally, I think it would give people more tools for going after the purveyors of misleading content. Either they would need to have a disclaimer, which could be pointed to for those that accepted the content without reservation, or they could face repercussions.

I see no problem with forcing people and organizations that purport to be representing a real situation but are instead presenting a view of that situation ideally suited to their own narrative to note they are doing so. Just because we've been conditioned to be tolerant of it in our media does not mean it's acceptable or needs to continue as it has.