MATLAB: Change or Add to greyed-out areas in App Designer

greyed-out userdataMATLAB

In the Design View, when I add a UI control, such as a Tab Group, it auto adds code such as:
% Create TabGroup
app.TabGroup = uitabgroup(app.UIFigure);
app.TabGroup.Position = [13, 296, 540, 96];
% Create FirstTab
app.FirstTab = uitab(app.TabGroup);
app.FirstTab.Title = 'First';
I want to add another line to this greyed-out code, such as this:
app.FirstTab.UserData.ID = 5;
When I click on the Tab in design mode, it doesn't show all of the properties, such as "UserData". How do I add UserData to a Tab, when the code is greyed-out and won't let me change it?

Best Answer

You do that by adding callback startupFcn which executes after component creation.
If you are on Editor tab, click on Callback and you'll see it on when you select UIFigure component.
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