In project file I import my own target file
<Import Project="Build\CopyDependencies.target" />
and later I call target from that target file
<CallTarget Targets="CopyDependencies" UseResultsCache="false" />
If I edit CopyDependencies.target file I have to reload whole solution and only then changes to CopyDependencies.target take effect. I believe it is some sort of build definitions caching in Visual Studio? If it is, maybe it can be turned off?
Thanks @KazR
Here is a smaller Solution that you can insert into your .csproj file
Problem solved