I tried FrayCheck on a quilt once in a couple places due to cheapy fabric wearing out 1/2" in from the seam. I would not recommend it. It makes the fabric super stiff. It can be sticky & pick up lint while drying &, honestly, it doesn't do a very good job.
You can definitely make a little applique piece to sew on. The other option (especially if it is already partially quilted) is to order Iron On decals.
I ordered a bunch of little 1/4" Iron On button decals from this place for a McCall's baby quilt (McCall's thought it was a good idea to put forty-two 1/4" buttons on a baby quilt so I figured out a substitution). They were fantastic! I grabbed a screen shot of buttons in the colors I wanted from a button website. IronOnSticker.com not only perforated the button, but also 2 tiny buttonholes in each of the buttons. I was able to run a decorative stitch between the buttonholes for an amazingly realistic look!
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I tried a larger 2x3" sample decal they sent on a rotary cutter oopsie & it worked great! Washes fine, just can't put it on high heat in the dryer, but I don't do that with quilts anyways. And you cannot iron it directly -- you have to carefully follow their instructions about using their special paper & a hard surface. Once they're on, they're definitely set. Here's their website if you're interested:
https://www.irononsticker.com/promotion-c-1239.html