States on Master slide being changed by variable change

Here is my question.  I have some buttons on my master slide that open up other  content.  I would like to have the button change from hidden, to normal based o the change of a variable on a slide.

So for example, if I want a learner to have access to a 'pirate chest' which is accessed via a button on the master slide but they can't have that until they have walked the plank which is the testing of part 3 of the module, is it possible to have a variable control that.

i.e. if status of completedmodule3  = true then change state of pirate chest to normal?

thanks for any help.