Is it possible to split an active subnet in aws?

I created a VPC thinking I wouldn't need subnets. I just gave the vpc a CIDR range like 192.168.0.1/24 I then created a subnet which matches that exactly.

Low and behold RDS requires it's own subnet. What happens if I delete the existing subnet and replace it with two /25?

Will the active instances become unhappy if I delete their subnet? Will they simply not notice or care?

I can't seem to find documentation on this and I'd rather not simply try it and see what happens.

It is not possible to change the CIDR block for a VPC. So if you have created the VPC with 192.168.0.1/24, then that's as big as the VPC can get. You'll have to re-create the VPC to get more space.

Also, it's not possible to change a VPC subnet. You can only delete it and re-create it differently.

On top of that, it's not possible to delete a VPC subnet that has any resource inside it. So you'll have to delete all RDS instances, EC2 instances, etc. that are in your subnet first, then you can delete the subnet.