Are you talking about sewing one on top of the other? Interesting.
I've seen the regs, but is it uncommon to do velcro with the right breast so that the squadron patch can be changed more readily?
Yeah, just put the new one on top of the old one, leaving the rocker of the old one showing, so you get a bit of history. I've seen folks do it with their green jackets with embroidered patches.
I've seen a few folks do the velcro+leather patch, but I don't think it looks very good and I think it kind of defeats the whole point of getting a leather patch. The leather patches are stiff when they're new, but if sew them directly to the leather, they get real soft with wear and look real good. If you have a leather patch on velcro, it can't break in as well.
Most people will either sew the leather directly on or just not have anything on the right breast.