No- this is two separate things. We're appealing, but not expecting to get anywhere, so preparing for high school life. I am just interested to know what sort of an academic peer group he'll have. Not something I intend to bring up at the appeal!
It looks as though some of those secondary modern schools do better by their high achievers than they do by their middle and low achievers. That is quite surprising to me: it seems they fail the students they are supposed to serve but do pretty well by students who were more suited to the grammars. But it's hopefully encouraging for you in the event your appeal is unsuccessful.
I imagine most of the students who do well at GCSE at a secondary modern would move on to one of the grammars for sixth form?