If you want to change global threshold, you can simply use "globalThreshold" attribute on <nlog /> element.
Simply:
<nlog globalThreshold="Info">
<!-- messages below Info level will not be logged -->
</nlog>
However, by simply lowering log level from Info to say Trace, you may easily get overwhelmed by low-level tracing messages you don't care about. So you will probably find it more convenient to re-enable logging at individual logger or for the entire namespace. To do so, you can add a line like that at the beginning of <rules> section:
<rules>
<logger name="My.Namespace.*" minLevel="NewLevel" writeTo="targets" final="true" />
<!-- other rules follow -->
</rules>
It overrides logging for all loggers whose names start with My.Namespace with the new log level being NewLevel. final="true" is there to say that no further rules should be processed for those loggers.
One trick I like to apply whenever I want to keep my logging configuration different for different servers is to use <include />:
You can do this:
NLog.config:
<nlog autoReload="true">
<targets>
<!-- define targets here -->
</targets>
<include file="NLog.${machinename}.config" />
<rules>
<!-- define default rules here -->
</rules>
</nlog>
On top of that need one extra file for each machine where the application is running. With this setup, you can put local overrides in NLog.${machinename}.config where ${machinename} resolves to the name of your machine.
You can try using other layout renderers here as well, and for example use includes based on environment variables:
<include file="${environment:MYLOGFILE}" />
or store included log file name in registry:
<include file="${registry:HKLM\Some\Path:value=MyValue}" />
