Both the dealer and I have by mistake overfilled my coolant a few times and everything seemed to be okay, never leaked or anything. I also have never in my 6 years of ownership added distilled water. I just top it off with 50/50 toyota stuff, around 100k I do expect to do a flush. I originally planned on getting the super awesome jackson dual radiator/oil cooler, but due to other financial strains I can no longer afford that radiator
On a side note, does anyone know if the J02 recall involves replacing the coolant? I don't think it does but seems worth asking.