Although not difficult to perform the installation, drilling incorrect size or not perfectly perpendicular, or retapping threads off center, would mean pulling the head.
The grease on the tap is to hold the shavings before they drop into cylinder, but invariably some does, besure to only go down a short distance, remove tap, clean shards, go in again a little further( DONT RETHREAD IN ONE SHOT)..an air hose will blow most of it out if intake valve closed and exhaust is open. The few particles that remain inside "should" just blow out on startup. If its anywhere near time for a valvejob or timing belt, I'd consider pulling head for best results...
Use anti-seize compound on all aluminum heads, or removal of the stuck plugs will pull out the threads. It may not have happened during reinstallation, could weel be during old plug removal. NEVER REMOVE plugs from HOT HEAD! Let it cool first.