The SD cards can in general be swapped around Raspberry PI cards.
The MAC address is stored in the network adapter on the Raspberry PI, so unless you change it, each raspberry PI will have a uniqe MAC address.
Default IP configuration is to use DHCP. This usually causes the the address to follow the raspberry PI card, since the router will remember which IP address it used to have, unless the card has been offline for some time. Some routers forgets this information on reboot. If the router does not have old information about the MAC address from the client, it can use the hint sent from the client before deciding which address it shall have. The client usually hints about which IP address it had last time it was connected. When moving SD cards between raspberry PI cards, this hint will follow the SD card, since it is stored in a file.
If you configure the IP address to be static, then the address will follow the SD card, since that is where you store that information:
https://wiki.debian.org/NetworkConfiguration#Configuring_the_interface_manually
Stian