He made the divorce of his wife conditional upon her doing something then he gave her permission to do it

Praise be to Allah.

The fact that you gave her permission does not cancel out the divorce which you swore would take place or that you made conditional upon this stipulation that you mention. Going back on your word does not help you at all, and the divorce remains in effect, if she did what you wanted to prevent her from doing. If what you intended by divorce was only to stop her doing it and you did not intend to make her divorce conditional upon it, then you have to offer expiation for breaking an oath (kafaarat yameen), because this is the same as an oath. 

But if your intention behind what you mentioned was to make divorce conditional upon her doing this thing, then divorce has taken place, if she did that on which it was made conditional. 

If there were no previous divorces after which this would bring the total to three, then it is a revocable divorce and the husband has the right to take her back so long as the ‘iddah has not yet ended. But if there were previous divorces and this is the third, then it is an irrevocable divorce and she is not permissible to him until she has been married to another husband. End quote. 

And Allah knows best.