Set flag to 1: Lua

Use an offset (a 'free for general use' offset, e.g. A000 as UB). For your 3 physical buttons, assign each of these to set a value in the offset (e.g. 1,2 & 3).
On your encoder assignments, add an offset condition to that offset, so only the one of the assignments (for VHF, ADF and squawk) are triggered. You can then set the offset to the required initial value in an ipcReady.lua script.

Thank you for your help. So there is no easy way to know the Numbers of this flag ? I am not good enough to redoo all the progammation with offset. 

Posted by: @guit32

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So there is no easy way to know the Numbers of this flag ?

What numbers of what flags? What is not clear in the documentation? As it says, you can use flags 0 - 255.
But why? this won't help you.

Posted by: @guit32

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I am not good enough to redoo all the progammation with offset. 

How are your two rotaries currently assigned? That is most of the work.
Assigning your 3 buttons (to Offset Byte Set) is straightforward.
If you already have your inc/dec assignments for VHF, ADF and squawk then it should be pretty straightforward to add an offset condition on those. If you show me how they are assigned, I can help.