AutoCad :: Stretch Multiple Rectangles At The Same Time

II have been creating rectangles using rec and because it is a polyline I get the "midpoint" nodes which I need to keep. I often have to modify these by increasing their length or shortening them, large numbers of them at times. Currently I have to select each "midpoint", of the rectangle, one at a time in order to change all of their lengths at one time.

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I am trying to find a faster way to select the "midpoint" of several rectangles or some other way instead of the individual method that I have been using. I've tried trim, extend, and stretch. Maybe there is another that I am not considering.

Trim removes the bottom line completely and retains only 3 sides so this doesn't work.
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Extend does the same thing and stretch works very different than what I am trying to do.

This is my exercise:
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