KeiHin definitely peened them, there's a cross patterned die mark flattening out the thread extending through the rod. I file this bit off before removing the screws. I managed to unscrew one without filing, but it's quite tight and the Philips/JIS heads do like to strip. The only way this peening could have been done is with some sort of clamping tool ... which I don't have one of.
I found SS button head allen screws to replace the factory Philips ones. Sorry I don't know the thread size offhand. I screwed them in with loctite, hoping it isn't attacked by gasoline (the area behind the choke plate gets wet in full choke use). Probably I'm insane but I thought the tiny button heads would offer less airflow resistance than the Philips ones I could find. The OEM screws are not a "service item" and are not available from Honda.