I presume the panel will have to change the status of the appeal....
Strictly speaking, it's the admission authority that would be changing the case, not the panel. (As with any appeal, the panel would, of course, have to decide whether the authority has got a case.)
all the paperwork received up until today stated it was a normal (non-infant class size) prejudice appeal
In that case, the appeal - in my view - shouldn't really be proceeding, because you've not had advance notice of the authority's ICS case, and time to re-consider your own. I think this would amount to maladministration.
Whether you would have anything to gain from requesting an adjournment is another matter because, as you realise, the chances of winning an ICS appeal are very slim (certainly in terms of personal circumstances).Unless
yours is the only appeal, what puzzles me is why they wouldn't have included an ICS case as a precaution. After all, only one Reception appeal would have to succeed for the combined class to reach 30, and any remaining Reception appeals would instantly become ICS.