Notice: this information was written when Microthemer version 2 was current. On Dec 26th, 2014 version 3 was released with a completely new interface. Some of the information may be redundant, but as much of
the functionality remains the same in version 3 we haven't deleted this post.
I suspect that a client will request to transfer to another designer soon. I do not want them to be able to have unrestricted access my microthemer license for free but ethically I cannot remove it either.
How can I leave them with microthemer but prevent updates or copying to another website?
You could do what you’ve suggested. Another (possibly easier) alternative would be to switch Microthmer into free trial mode by submitting a blank value on the validation form and then adding the following code to your functions.php file: