That's a good question, and I don't know the answer. Part of me says to wait until next year, because your grasses won't be in the dormant stage yet, and all the literature says not to mess with them (dividing, etc..) when they are in flower.

The other part of me can't think of how it might damage them. Some will probably grow back a bit before dormancy, but that shouldn't hurt anything. If they're cool season grasses, it definitely won't hurt them, but I can't say what will happen to warm season grasses.

Let us know what you do, and how it goes.

Good luck with the surgery.

The first two articles found with the new Google Instant Search say wait until spring. I would think waiting would provide protection form the elements. Some grasses look quite attractive in the wintertime.