Adding RIO Module

I have an existing 8 position Allen-Bradley RIO rack with 3 blanck spaces. I want to add a 1794OF41 analog output module. Is there a trick to it, can it be done "hot" or do I need to shut the system down and configure it. I know that I will probablely have to write a BTW - BTR circuit to get it to work.

A little confused about the rack question, a flex I/O module does not use a rack it just plugs into its own base and the preceding module or adapter. BTW/BTR's will depend on the platform used ( PLC,SLC or Logix)
You cannot install "Hot" ( should not install "Hot")

http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1794-um008_-en-p.pdf