You need to log into the actual device and make changes over there so that the same can be applied in the Add Node Details page.
this scenario is not supported. You can create new “Network Sonar Discovery” and set “SNMP Community String” for selected ip range (see documentation http://www.solarwinds.com/documentation/Orion/docs/OrionQuickStartGuide.pdf). Other solution is “FREE SNMP Enabler For Windows” http://www.solarwinds.com/products/freetools/snmp-enabler-for-windows/enable-snmp.aspx, which can configure multiple SNMP devices, but only for windows based solution.
Regards Tomas Pospisil