Hide- Show - Disable custom navigation buttons.

Do it with variables.

For example, create a T/F variable named "disableNav" initially set to "False." 

On your master slide, create a trigger to set your button to disabled state when variable "disableNav" changes, if value = "true."

Create another one to change its state to Normal when that variable changes, if value = "false."

I hope that helps. If not, see if you can share your file.