I think I kind of misread the question too...the c.g. range is based on the wing planform. The forward limit is can be manipulated with length and size of the horizontal but the aft limit cannot. If your spar shifted in relation to the leading edge, you should base it on the leading edge. That being said, it is very easy to change the sweep of the wing which affects the location of the mac. I think everyone should calculate their own mac...it's easy to do with the site I gave before...you can measure the sweep with a chalk line and a plumb bob.
https://sites.google.com/site/mykr2stretch/ https://sites.google.com/site/mykr2stretch/parts-for-sale
