I tailor my own squat suits. I’ve yet to do anything to a bench shirt though. According to the new rules, if you shorten your straps and the area shortened is greater than 3 cm, it must be sewn so that the extraneous material is to the inside of the suit so that you avoid the unsightly ‘bunny ears’ look you get when you leave the material on the outside.
I’ve tightened a few suits at the hips as well. Turn the suit inside out and just sew along the original manufacturers seam pulling the material in a bit. Don’t create new seams or pleats and down’t sew the material back on itself creating a reinforced seam.
This is a picture of the shortened straps…