From our internal KB article, which I adapted from @jay-cummin's post here, and then wrote some scripts to make using them quick and painless:
As many of you have discovered, at times you can’t switch from ArcGIS Basic to ArcGIS Advanced because the radio buttons in ArcGIS Administrator are disabled:

Fortunately there is a workaround, set the license level in an environment variable first and then run ArcMap/Catalog. We’ve placed scripts for this in Z:\Tools [GitHub]:
ArcMap-Advanced.bat
run ArcMap using Advanced (ArcInfo) license
ArcMap-Editor.bat
run ArcMap using Editor (ArcEditor) license
ArcMap-Viewer.bat
run ArcMap using Viewer (Basic) license
I actually prefer the workaround to the original method: you don’t have to close all your sessions down first just because you want to run an Advanced-only tool for 5 minute job like Create Random Points, and you can run Advanced and Basic side by side at the same time.
You can also set license server this way. Port number and @
are optional. (ref):
ARCGIS_LICENSE_FILE=<TCP/IP_port_number>@<license_manager_hostname>