I have a commercially made throw pillow that I think would be really improved by adding some color-coordinated piping/trim/etc. around the edge. Is there a way to neatly add on some trim that wouldn’t necessitate me deconstructing and then re-sewing the entire pillow? I’m concerned it won’t end up looking as professionally finished as it does now if I go that route.
The only way I can think to do such a thing without disassembling would be if you didn’t mind the case becoming a bit smaller. You could turn it inside out and carefully pin the trim between the fabric layers of back and front, then stitch at the edge of the piping or braid which would end up being that much further in from the seam that is already there.
I do think this is going to yield the same sort of result as opening up the seams though. The seam that shows will be one that you sewed. If you feel daring enough to try it, watch a couple of videos on how to sew corners on cushions and go for it.
Alternately, if you want to add a different sort of trim to spruce up your cushion, tassels on the corners are nice. Or a hand stitched line of embroidery close to the edge, or a hand stitched line of ribbon, etc.
They do sell cording trim that has no flange that could be hand sewn on, but you’d have to get creative with finishing where the ends join. Plenty of fringe and pom trims are meant to be applied to the surface have a finished “flange” so you could hand sew or even glue those on and they would perhaps be easier to disguise the join.
Adding onto what others have mentioned, You could make your own piping that is a finished loop with no flange and hand stitch it down.
You could also just do some couching of a round trim around the edge, so you wouldn’t have to deconstruct the pillow. In contrast or complimentary thread.