i have been doing a lot of research on control net lately. I have a project dealing with it. You do have to take it down to add anything. It makes you go into program mode when you go into rsnetworx. check out http://literature.rockwellautomation.com/idc/groups/literature/documents/um/cnet-um001_-en-p.pdf I have been reading this all morning. Also look on youtube there is some stuff there.
This looks like an input card if I am not mistaken. You shouldn't have to do anything with the controlnet network. If all you are doing is adding an input card you should be able to add it to the hardware configuration and push that to the PLC. I would make sure you were down when you did this. You should have to go into program mode to do this. As long as the hardware configuration is correct you should be ok.