Another option to consider is to word the new wrap plan document in such a way that it includes language to terminate the previously existing plans. This information could also be included in the SPD which would indicate that the previous plans (complete with their plan name and number as stated on the 5500) have terminated and are superseded by this new wrap plan. This may be less confusing to participants than sending them a termination SPD.
As for the resolution, this could be handled the same way; the enacting resolution could reference the termination of the earlier plans.