How to alter the Skirt:
Back Skirt: trace off the skirt pattern and lengthen the Skirt to floor length (plus hem allowance),
Front Skirt: Right side Front create a copy of the lengthened back skirt and draw a vertical line approx 1/3 of the way across the skirt to create the split. Cut these out then retrace each piece and add on an allowance to create a fold back facing of each side of the split, which you could hand hem. I would allow for the same amount for the facing as you allow for your hem.
Front and Back Skirt: Trace off another copy of the skirt pattern and shorten to mid thigh length (Plus hem allowance)