Well, having tried the option of creating a special plan I have two problems; if I choose a Merchandise type plan, I cannot choose to display the fields I've created for details about registrants instruments etc; however, if I choose a subscription plan, however I configure it, users who already have subscriptions (most of the likely bookings) can only see the plan if I choose 'allow upgrade'; then, of course, they get a message saying how much more it will cost if they upgrade, which is not what I what I want at all, so I'm still left pondering this ...
clearly, it's a merchandsie plan that I need; is there a way I can collect the extra information I want, by displaying the new fields, or by some other means?