Hi SB888, and welcome!
I am sorry he is getting upset about this - it is a very difficult time for all the children.
Guest55 is entirely correct in the essentials. If you change your preference now your application will not be considered in the first round of allocations and you risk losing both RGS and JHG.
Leave your preferences as they are, and when Allocations Day comes you will surely be offered RGS. You should accept that place and then apply to go on the waiting list for JHG. Given that first preferences for JHG are down this year - see my post here viewtopic.php?f=12&t=23939
- it seems likely that it will deliver a place in a later allocation round. Allocation rounds take place at 6 weekly intervals from 1st March.
In the meantime, I think you should consider why you and your husband initially chose RGS over JHG. Sometimes parents have to be the people who know best, and if you had strong reasons for that choice at the time, you need to revisit them and then discuss them with your son.
He is bound to view changing schools with trepidation and to worry that he will be left out locally, but he will soon make new friends at RGS, and be able to keep the friends from his old school. I know of a couple of children in that position, and in some ways they have the best of both worlds - the right school for them, plus long-standing local friends.
As Guest55 says, I would email Admissions because there are a couple of slightly conflicting statements in their Admission brochure. One states that you can go on the waiting list for "a higher preference school that you have not been allocated", and the other says that you can "add new choices", or words to that effect.
I feel sure that my advice is correct, but please do check!