Convert a PCL to a regular Class Library

The differences will be in your .proj file.

Having tried it myself you will have to do all of the following;

1. Remove the <TargetFrameworkProfile> element
2. Remove the <ProjectTypeGuids> element
3. Change where you have #2 (below) for what I shown in #1

1. Regular class library

<Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />

2. Portable class library

<Import Project="$(MSBuildExtensionsPath32)\Microsoft\Portable\$(TargetFrameworkVersion)\Microsoft.Portable.CSharp.targets" />

Use VSCommands, it has as a build in functionality to convert Projects to PCL. Right mouse click on Project and convert. It´s free and part of Visual Studio extensions http://vscommands.squaredinfinity.com/Features-SolutionExplorer

Update 2016-10-12: Above link is dead. The tool has been rewritten for Visual Studio 2015 and can be found here: https://visualstudiogallery.msdn.microsoft.com/c84be782-b1f1-4f6b-85bb-945ebc852aa1