Include File in NuGet package on Build, only if it does not exist

A while ago I asked this question:

Including a Folder in NuGet Package and have it install into project as file .netcore/Razor

The answer to which has got me most of the way where I want to go, but the trouble is rebuilding or updating the NuGet package in my projects is now overwriting files that are user-editable.

I feel the answer is somewhere in the .props file but I am not sure how to achieve it:

<Project>
  <Target Name="CopyFiles" BeforeTargets="Build" >
   <ItemGroup>
      <File  Include="$(MSBuildThisFileDirectory)..\Pagesettings\*.*"></File>
   </ItemGroup>
    <Copy SourceFiles="@(File)" DestinationFolder="$(ProjectDir)Pagesettings"></Copy>
  </Target>
</Project>

The Target tag has an optional attribute Condition. I am guessing that somehow this can be used...?

So, to clarify my question:

From my original question linked above I have a NuGet package which when downloaded creates a folder called PageSettings, into which is copied a bunch of default JSON files containing PageSettings from my NuGet package. NOTE; these files initially appear in Visual Studio as linked files. They are not actually copied to the directory until the project is built.

However, the purpose of these PageSettings files is to be a default , or if you like an example, of PageSettings for users of my NuGet package. Once installed, the user can and should change these .JSON files, so now when their project is rebuilt, or if there is an update to the NuGet package available which they install, these JSON files should NOT update/install.