As long as the APs are on the same subnet/VLAN you should be good. All of the IAPs perform a master election, and any of the APs can take over as the Virtual Controller. You can prefer one to always become the Master when it is up. See image below. I personally would just change the IP on one of the IAPs, then change it to become the preferred master. Once that's done, change the IP's on the rest. You can also make sure that your VC has the same address no matter what IAP takes over with the following steps:
To specify name and IP address for the Virtual Controller:
1.) At the top right corner of the Instant UI, click the Settings link. The Settings window appears.
2.) Enter a name for the Virtual Controller in the Name text box.
3.) Enter the appropriate IP address in the Virtual Controller IP text box.