Increase the number of buttons

[mega-TWZ]

My Game Controller is Fiydigi Vader 2 . It has four back buttons and two additional front buttons ("C" "Z") .
In the AntiMicoX 3.32, "Controller Mapping" didn't reserve their place . They can map Strings in a preemptive way ( Should I describe it this way, I have just contacted AntiMicroX, and I do not know the underlying logic, String, API or SDL2 ) .
"Options"--> "property"-->"buttons" can detect these 6 buttons, but cannot respond ( blue ) unless in a preemptive way .
The main page can also show them button 16～ button 21, as if they are eagerly waiting to map a keyboard letter。
How should I read the source code and modify it，detect --> respond --> map a letter。

[pktiuk]

Answer to this question can be found in related issue: #694