You can, using dyndns. But your router must support that.
Uhh, i don't think you quite grasp the idea of networking /subnetting. You could use 4 different subnets like this:
192.168.1.0/24
192.168.2.0/24
192.168.3.0/24
192.168.4.0/24
All of them have a 255.255.255.0 subnet mask (hence...