You cannot use dequeue because the return cell is a new instance of the cell and not the cell displayed.
Your are two way for change the button state.
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Transport your (IBACTION)method in your custom cell class and not in controller class and release legacy code. If you need to update data between CustomCell and controller create and invoke a delegate. 
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The second way is to reload the Cell of UITableView after setting necessary values for presented the well state 
solved How to disable a buttons in a custom cell?