I wonder if there is a way or a workaround to have the config files in the following structure:
App.Config
<configuration>
<appSettings configSource="AppSett.config">
<add key="test1" value="test2"/>
</appSettings>
</configuration>
and my AppSett.config will look like:
<appSettings>
<add key="test3" value="test3"></add>
</appSettings>
No, you cannot use external file with partial info to link instead of the default config structure. Config files are special files that conform to config schema and this you cannot use them in the scenario you described.