flex I/O module re-configuration

I have a flex i/o rack,(ip scanner [0],input card[1],output card[3]) all is functional and operating. I want to use output at this time and this is all programmed and ok. My problem is without shutting the line down,I need to change the output card configuration online with out any problems. The current out put was setup with a 8 point card along with software
but the base back plane is a 15 point. I know I can change cards on these but not about base. Will this fault the module?Do I need to inhibit first? If u need more details let me know. Thanks.