If I can suggest another method.

If you only want an inch or so, don't rip the thing in two. Leave the center seam intact. Remove the top stitching from the two "out" pleats and the two "in" pleats that make up the reverse box pleat at the center.

rip out only enough waistband to be able to turn it inside out.

reduce the amount of "reveal" of the two center back pleats and iron new pleat edges. re-Top stitch these.

then stitch the two pleats you just re-topstitched back down to the center seam in the Fell area.

Then iron new "in" pleats from the back and re-topstitch them.

Mark the amount of waistband that needs to be removed and turn the waistband inside out. Cut out or iron flat the excess fabric leaving enough seam allowance to sew it back together.

sew the waistband back on and your done.

This method leaves all the fabric intact in case you ever need to make it bigger.

It should only take an hour or two.