Transferring between the schools is easy.
If you really want to do Comp Sci in Engineering, i would transfer now for a couple of reasons.
First, it’s easier to transfer from Engineering to A&S, because engineers need a few more credits and the curriculum has lots of requirements, many of which need to be done in a specific order. It’s harder to catch up transferring into Engineering.
Second, engineers get to register for courses before A&S, which can be a big advantage.
Third, the Comp Sci major in engineering gets more respect in the marketplace than one in A&S.
Fourth, engineers’ track record for having jobs waiting when they graduate is really good.
My kid went to Tufts Engineering (I’m an A&S alum) and had a job in place very early, which made for a much more enjoyable senior year.