To add to this question: I would not only like to be able to switch between v3 and v4, but also between v2 and Orion as there are many older applications that expect v2 and newer ones that only work with Orion. I have found this old post:

Somebody asked for a way to be able to switch between v1 and v2. I assume it should still be possible to install two different versions into different directories and then, assuming that the newer version was installed after the older one, to stop the newer Leap Motion service and to start the older one from the command line by calling the older service executable? Does this still work with v3 and v4?

Or is there a simpler/more convenient solution?

You can copy the old version to a different directory before installing the new one. So, even if the installer automatically uninstalls the old version from the original location (under 64bit Windows for v1 and v2 that would be "Program Files (x86)\Leap Motion\Core Services"), you still have a copy of it. Given that starting the service from the command line by calling the executable still works with v3 (haven't tried that yet), you should still be able to stop the new service and start the old service. (This also assumes that the same set of hardware drivers can be used with both versions and it is sufficient to just switch the service.) You could then write batch (or PowerShell) scripts that take care of the switching.I agree, however, that a more convenient solution for switching versions would be desirable.

I hope somebody from Leap Motion will chime in and let us know whether
a) it is still possible to switch between v2, v3, and v4 using this approach and
b) whether there is an alternative, potentially more convenient, way to switch between versions.
Being able to use an older version for older applications is essential due to incomplete backwards compatibility.