In Elder Sign, can I free a focused die?
No.  Once focused, a die may only be used to complete a task using its locked side.

This is not specifically mentioned in the rules or the FAQ sheet - however, based on other rulings in the FAQ, it is clear that not being mentioned in the RAW is not considered proof positive that a rule doesn't exist by the creators.  Focused dice are especially limited in usage, and they seem to be intended to be used only in a very specific way.  I believe you should go with the same ruling as the video game.