Having way too much oil in an engine can cause problems when the oil level is high enough for the moving parts in the engine (like the crankshaft) to splash through it. When this happens the oil foams and can cause the oil circulation in the engine to fail (the oil pump wants to pump oil, not air).
I don't think a 1/2 quart over the full line is something to worry about. I have seen this happen before without any engine problems. If it really bothers you, just put a drain pan under the engine and drain out a little oil. It will make a mess when you try to put the plug back in, but nothing that can't be cleaned up.
I did notice when I changed my oil for the first time that it didn't take as much as the manual stated (and yes, I changed the filter too). I wonder if the manual might be off?
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2001 IS300
Spectra Blue Mica/Ivory
LS, LD, HH, SR, 17" wheels
2000 Jeep Grand Cherokee Limited
4.7L, QuadraDrive, UpCountry
Patriot Blue, Fully loaded