How can I switch back and forth between Unity Pro and Free?

I understand that the terms of the Unity license are that as a developer I am supposed to use either Unity Pro or Unity Free, but not both. However, if I am a Pro developer who wants to release a package on the Asset Store that is compatible with Unity Free then I need to be able to test it with Unity Free first.

How can I switch back and forth between my Pro license and a Free license without reinstalling and without using up the two activations I get per Pro license?

I suppose you’d have to get a different computer with Unity Free installed, and try using it there.

You can use the -force-free command-line option. Even if this itself is violation of the ambigous EULA, I am using it because it exists as legtimate option, and the Unity’s EULA seems ambigous at some places.

Check this for other commandline arguments: Unity - Manual: Command line arguments

I know this is an old question, but I’m putting an answer here, in case it helps somebody else. The following instructions are relevant to Unity 5.3.2 on Windows 10, and assumes you have already installed and activated Unity Pro.

  1. In C:/ProgramData/Unity, rename your Unity_v5.x.ulf to something else, indicating that it is the pro license.
    ( Unity_v5.x.ulf.pro will do).
  2. Run Unity.
  3. Select “Personal Edition.”
  4. Click “Next”, etc.
  5. There should now be a new Unity_v5.x.ulf in your C:/ProgramData/Unity folder.
  6. Rename this ulf file, indicating that it is the personal license. ( Unity_v5.x.ulf.personal will do.)
  7. Whenever you want to use Pro, copy the Pro ulf back to Unity_v5.x.ulf. Whenever you want to use Personal, copy the Personal ulf back to Unity_v5.x.ulf. You may wish to write a script to automate this.

Try this. Create a second account at unity.com. Then in the upper-right corner of the unity IDE, click on Account and sign out. Then login with the new account. That new account will only have a personal license and that license should be used. To go pro, just logout and back in with your pro account.