I have added more fmq to a quilt after it was bound with no ill effects. I've also heard from people who quilt competitively that they've added more fmq to a quilt in response to judges comments. But that was a little here, a little there, so it may matter how heavily you're planning to fmq. I would check the bottom regularly to make sure no pleats are being quilted in, but I'd say go for it.