Another thought:  If it's a figure you won't need to rebuild.

For a single change like this, you can just edit the CR2.  Find the paragraph for Flap2, then scan down until you see

parent Box

or it might be

parent Box:1 or some other number.

Change this to

parent Flap1  (with the :1 if it was there)

Then scan down until you find

addChild Box
   Flap2

Change this to

addChild Flap1
   Flap2

While you're in the CR2, also change every bend 1 to bend 0.

Resave the CR2.  As above you'll still need to readjust the joint centers.

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