1. Get a fresh copy of the program (while online, save and upload all data).
2. Go offline.
3. Save as...with a new name
4. Go to the I/O configuration and make the required changes to match the new intended configuration.
5. Suppose for the sake of an example that the NO8I is replaced with NO4I in slot 5 and a new NO4I is installed in slot 6 where no card existed before:
Search and Replace the following addresses in the offline file:
O:5.4 with O:6.0
O:5.5 with O:6.1
O:5.6 with O:6.2
O:5.7 with O:6.3
6. For this step, I would need to reference the manuals to give exact details, but you may or may not need to modify the logic to ensure the configuration data for the cards are correct. Some of hte SLC analog cards require that you have the proper values in the extended data configuration words in order to set up the ranges properly. I believe RSLogix500 may be able to do some or all of this for you, but you will need to review what is going on with those data points in the old program.
7. Power down the SLC
8. Switch the keyswitch to program mode.
9. Install the new cards and rewire the analog signals.
10. Double check your wiring and make sure that if external power is required, you have supplied it (I don't know off the top of my head if that is optional or required).
11. Check the wiring again. Better yet, have a competent partner check your work.
12. Power up the SLC with the keyswitch in program mode.
13. Download the new program.
14. Put the keyswitch back in run mode and then to remote run mode (if that is where you want it during normal operation).
15. Verify that everything is working as intended.
I like to switch to program mode before making I/O changes so that the PLC does not fault. I had at least one situation where I caused a fault by powering up with the wrong I/O configuration and the SLC freaked out and would not let me get online to straighten things out. I found that not faulting the SLC may save a little headache at least every now and then, but it is not a show stopper if you leave it in RUN mode and then have to deal with the extra steps of clearing the fault before downloading the corrected file.