Menu button in master slide hidden on some slides because of my graphics: how to access it?

Good day Helene. 

I just had to do some finagling with a similar project. If the issue just appears on some slides then this solution may be of help. The more slides the more work. 

You are absolutely correct that you can't directly access the layers on a Master Slide (may want to add that to your list of suggestions to the SL dev team). But here's how you can work around that little issue (and there are probably more ways but this is how I did it).

1. Create a new T/F variable and give it a name (OpenSesame for instance). 
2. Go to the Slide Master and create a new layout (or duplicate an existing one) and add a menu layer and include your menu. Make sure to include a way to close it (I know you've probably done this but I'm including it for anyone who follows). 
3. On your menu layer add a trigger that sets your variable to false when timeline starts (this resets the variable each time it is used).
4. On the base layer of your slide master add a trigger that shows the menu layer when user clicks your menu button (which is also on the base layer). 
5. On the base layer add a trigger that shows the menu layer when your variable changes, on the condition that the var is equal to true. This is what you'll be triggering when you add your pseudo menu button on your pages that have the menu covered. 
6. Use the layout you created in step 2 for your pages that need menus. 
7. For pages that the menu button is obscured by graphics place a duplicate of the menu graphic over the top of the one that is obscured. Set a trigger on it to set your var to true when the user clicks. This will trigger the base layer to show the menu layer. 

It's a lot easier to follow if you can see what I'm talking about. I've included a sample file for you to see how it all comes together. 

Hi Michael

That is very clever! Quite a lot of copy-pasting to do, but at least I will have something that works, thank you so much!