FWIW, (Not to be stick in the mud here)

You can blend the clear, but most shops don't do that.
They blend paint but they will reclear the entire panel and everything else that touches it.

In your case that would mean reclear the entire rear unibody..

Why cant you blend clear? or why shouldnt you?
In most every case because the resulting
"Blended" clear coat will be to thin where you "blend" it into the rest of the quarter panel.. that over time it will peel...
it will not hold...

With that said, people and shops still blend clear
coat. But usually they would only do it in very small places and usually on the lower portions of the car. NOT any large place (Like the middle of a hood) or the top of a trunk lid (or anything else exposed to direct sunlight...

To my (limited) knowledge I don't think any OEM advises to do that. (Blending clearcoat)...

Body shops that do it are usually operating under the presumption that you will not be keeping the fixed car for more than a year or two...

Anyway thats why blending clear is not really recommended...

If the rest of the clearcoat on the quarters/rockers, trunklid and rear w/s cowl and rear valence are in good shape...

You can prep your existing clearcoat very easily using a scuff pad with a scuffing paste (Like 3M-ScuffIT) and rinse with water...

Then reshoot your clear. You don't have to wetsand the entire rear unibody with 400 grit
to reshoot clearcoat...

Hope this helps...

If it were mine (and I know it isn't) I would
reclear the whole rear...two coats...
but that's just me....

Good luck to you either way..