Make a smaller hole?

I am still noodling about my ES4-B kit. I have been thinking about putting some switches where it would normally have knobs and visa versa. That leads to an interesting problem...

The pot holes come stock at 5/16"... that's a tad large for micro-switches, but I think I may have found some switches that have a bigger shaft that will fit...I hope.

The really tricky one may be where the three way switch would normally go. I'd like to put in a blend pot. Just got some...and they are the standard 3/8" shaft. That will be mighty loose in the giant 1/2" hole that is there for three way switch.

I know that making a small hole bigger can be tricky, but at least I feel like I know how to do that. I have no idea how to make a hole smaller in a piece of wood that is so thin. Hoping I can find a plastic spacer or something that will work...but wondering if others have found a solution to this problem already?

Plug and redrill. Since it is a hollowbody you MUST make sure there is plenty of glue around the plug and use a pilot hole first to keep the final drill bit aligned.

Never plugged anything that thin. How do you do it?

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The hole will only be 1/8" too big if your numbers are right.
Tricky to plug a thin top... I'd consider patching it up from behind and cut some veneer to fill
Alternatively you could plug with a section of dowel and redrill
Or use a slightly bigger washer or cover to simply cover the slightly larger hole

Stan is on the right track.
What I do is, as Stan suggested, glue a thin (2mm max) shim behind the hole.
Then I break out the trusty plug cutters and find a chunk of tree with a grain that matches as close as possible to cut the plugs from.
Leave the plug full length, glue it in and let it cure.
Once the glue has cured I then cut the plug flush with a flexible flush cut saw and sand.

That should still be thin enough to get a nut and washer on the pot shaft. I should be able to find a dowel that will fit, and the whole hole will be covered by a washer, so I might not even need DB's level of skill to pull it off. Always a plus ;-)

Knock up a stepped washer to take out the slop?