Can't adjust my half round sheetmetal part!?

Dear forum members,

I'am making a halfround sheetmetal part with flanges. (picture 1)
But when i try to change my diameter the flanges disconnect (picture 2)
And there is no other option then cntrl+z.

i used sheet metal loft to create a sheet metal pipe.
Then i use extrude to cut the pipe in half.
last but not least i added two flanges to my halfround pipe.

Is there a smarter way to create this design?
And how do i make my design adjustable in diameter?

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