<< Can I simply countersink them 1/8 to 1/4 inch, fill with an exterior
spackle, sand, then prep and paint the exterior as normal? >>
For a permanent fix, pull the nails out, replace with stainless steel ring
shank nails or SS screws.Since the problem will be more prevalent on the lower
courses, the proper repair shouldn't be too time consuming. There several kinds
of effective nail pullers on the market, mostly found at old-fashioned hardware
stores. Good luck.