Changing IP address of SQL Server 2008 R2
Changing the IP Address for a machine running SQL Server is not a problem at all.  You'll need to restart the SQL Server after changing the IP Address so that the SQL Server will start listening on the new IP address.  But that's it.

If no users actually connect to the machine then there's nothing else to do.

If users did connect to the machine they'd need to refresh their DNS cache on their workstations by running "ipconfig /flushdns" or by simply restarting their computers.

Unless you've done something very unusual with the TCP listeners within SQL there's nothing else that needs to be done with SQL Server other than the quick restart.