A neat trick for patching the screw holes left behind - use a old fashioned razor as your putty knife, it is so smooth you can get away without sanding as the razor is smooth on it's edge.
Use either finger nail polish remover or acetone (the active ingredient to polish remover) and a q tip to wipe/scrub away the Marine tex that isn't part of the hole. I'd put tape around the hole to limit the clean up.
No one but you will know it's there.
But you'll always know
You will need to look to where the current clam cleat is fastened, is it simply screwed in, or is it mounted with bolts etc.. that might entail removing the liner from the cabin/getting under the cockpit coaming. If it's simply screwed in now you and you can get to the underside go ahead and upgrade to a bolt with a big finder washer to offer more support.
Assuming you normally take a few wraps around a winch and the cleat is simply to hold the line it might not take much to hold it, but bigger is always better.