If you are talking about switching in a running session, not that is not possible.
NX needs to restart to get the proper connection variables for Managed mode.
Ronald van den Broek
Senior Application Engineer
Winterthur Gas & Diesel Ltd
NX9 / TC10.1.2
Building new PLM environment from Scratch using NX12 / TC11
For what it is worth, There is a command called rescue session. If for some reason you lose connection with teamcenter, you can use this to export your data, and reimport the data during a teamcenter NX interruption.