If you are only concerned with moving schools, based on a SEAS category, maybe you should re-consider moving schools to begin with.
I'll be honest, I moved schools for Year 12, and, funny enough, it would mean that I was not applicable for a SEAS category. (Under-Represented School).
It didn't phase me at all, as my new school was more academically inclined. Need to rephrase here but it was a ATAR, with SEAS 'bonus points' would be lower than if I had ATAR + Moved to a new school.
...
Not too sure if that makes sense, now that I read it. >_< <- Scrapped all that, I can't seem to convey, very well, what is in my head.

But there are more factors to consider, besides the SEAS category. Is your new school considerably bigger/smaller than your current school? Do you know if it's more academic than your current school? Do you have friends at your new school? Do you know how long it will take to travel to school?
I considered all these points before I took into account the SEAS category and, to be blunt, the SEAS category was not even a factor, for me, in moving schools.
EDIT: I feel inclined to make my post have more 'meat' to it, as I was in the same position to you, more than a year ago. Hmm, if you want me to elaborate why I moved schools, sure. (I didn't want to add it here as I guess it would be considered 'straying off topic', in consideration to your question. But you should elaborate further, on why you want to move schools. Is it your teachers? Your peers?
Frankly, from what you have said, you are only considering moving school's based on a 'weak' cohort. I did consider that but, for me, I said that I could just get Rank 1 in everything, if I were to stay at my old school. Hmm, it's a lot of pressure to do that as well. (Having talked to friends who did decide to stay at their school, rather than move.)
But it's like a double edged sword, if you do decide to move schools. (As my old school kept berating/parroting to me about, they wanted me to stay .. -_-).
If you do move to a more academic school, would you be able to keep up with the work? Could you manage being in a class full of students who
want to learn and are
not being forced there? (My old school was that most students in VCE did it for the 'Lols'. Not joking, they didn't care about who actually wanted to learn). For me, that was a very hard 'concept' to grasp in my head.

. Even now, I still have difficulties with being surrounded by people who want to learn. xD
Also, a slightly minor point, but you will have to build new relationships with teachers. I found all my teachers to be simply amazing, save for the start of the year. They didn't really seem to like me, as I was new and trying to get used to everything. I noticed preferential treatment from the students, who were already at the school, compared to me. I was 'denied' work but when another student asked, she was given it. This is definitely going to vary from school to school but it took awhile for me to get over the apprehension of asking for more work and, soon enough, teachers liked me. (But I have a pretty boring personality, so maybe that took awhile for them to get used to)

tl:dr: You will notice a difference between schools. A lot of factors to consider and you should elaborate why you want to move schools and what you want to achieve from it.