I had a look at the dress and underwear to be altereed. The stays(the second of the Hunnisett Tudor/Elizabethan ones) are simple to alter - unpick binding, undo side seams, take in 1" either side, losing a little under the arm, and re-stitch, and bind.
The pad on top of the bum roll will be shortened a little at the front, bones removed, rebound, and worn, without the pad, under the petticoat, to give a slightly more triangular shape. Petticoat, with attached stomacher, simply has the eye moved, and an extra one added for luck. The overlap thus caused - about 4" will help to bulk out the back of the dress a little.
I have already unpicked the bodice from the skirt. The skirt will be removed from the waistband (cartridge pleats,) and the "frill" will also be unpicked. Then the excess fabric will be re-folded, giving a shorter length to the skirt, and resewn to the waistband. The extra fabric will, again, bulk out the shape a little.
Then the biggie! Remove the sleeves, oversleeves and epaulettes and reserve! Unpick the side and shoulder seams, remove the binding all round, and reserve. Reserve the back for later, and recut the front. (There is enough material saved to do this, thank goodness.) Then put everything back together again, except for the oversleeves. Sew the skirt back to the bodice. The finished shpae should be more like this.
Wipe brow and collapse!