over filling any fluid is a no no.
Well, it depends on the circumstances. You don’t want to seriously overfill your crankcase, because the crankshaft will beat the oil into a useless foam. On the other hand, overfilling your windshield washer fluid won’t do any harm. It all depends on whether the intakes and pumps will mix air into the fluid, or cause some other problem. Follow the instructions and try not to go above the “Full” line. At the least, the extra fluid will be expelled and you will have wasted money and made a mess. Also follow instructions to purge air from any system, if needed (coolant, PS, brakes,…).