Primary choices change!

[FazedNConfused]

Hi there,
Just wondering how it works if we change our mind regarding school options after the deadline?
Applied for schools A and schools B.
Choice 1
School A- often oversubscribed, just out of catchment, so might not get in anyway

Choice 2
School B current catchment school, undersubscribed

If we get our first choice is it still possible to go for the choice 2 even after the deadline? School B has been undersubscribed for the past 4 years so unlikely to have no spaces.
Just wondering what we'd need to do should we want to go for our option 2 instead.

All due to uncertain housing situation- would prefer to walk to school but it's all unknown to us now where we'll live and that's the deciding factor!

The deadline for on-time applications has already passed so the first thing to say is do not make any changes now before you are offered a place on April 15th /16th. This especially applies if you are moving home
See what happens in April. If you get your first preference school then you should first confirm the place so that you have your fall-back school. You can apply off the waiting list for a place at your second preference school. Undoubtedly the admission office will query why you are now looking for a place at the second preference school as it would seem illogical to them. You need to explain that you have changed your mind and for various reasons would prefer a place at the second preference school. If you have moved or are about to move then you will have to tell the admission office when you ask for a place of the waiting list. If you have not moved then I would not mention any potential address change unless it is going to happen.