Can you rework the bottom of a sweater without redoing the WHOLE sweater?

I have a knit sweater that I wish had less stitches around the bottom half, so that it was tighter. It’s a zip-up. Instead of re-knitting the WHOLE sweater, is there a good way to redo the bottom and attach it invisibly to the upper half?

Yep, a couple ways but it involves cutting. Either cut the bottom part off and reknit it then graft it back to the top, or cut and reknit from the top to the bottom.

Thanks Suzeeq,
But how do you “graft” it back to the top?

Either way, you have a 1/2 stitch jog.

I’ve used both. But prefer to cut where the ribbing joins the body. And just reknit the ribbing. You can do it in one piece-front right, back & front left. I think it looks neater than grafting. You can do a few decreases when starting the ribbing, to make it snugger, if needed. Or you can work with smaller needles. I’d calculate how much smaller you want it first.

Another option is to make bigger seams on the sides.

You graft with kitchner stitch. Same method used to close toes on socks.

a bit off the wall but it worked
i crochet around the bottom of the sweater
and the sleeves
it was varigated yarn and it looked fine
i have done it on solid color
single crochet