I doubt you're weakening it.
I have a Raymarine ST1000 on my P26 and it's been there 6 yrs. (covered w/ tiller cover when not in use. We fashioned a custom made "hump" out of teak to raise the pin to the tillerpilot's height, and drilled a tight hole into which I epoxied the pin.
In 6 yrs. the hump-to-tiller joint (bronze screws plus thickened epoxy joint) is tight and so is the pin.
I could be wrong but think if you fill (use thickened epoxy) & redrill you'll be oK. Mine is coated with Cetol light & clear finish. After 5+ yrs. it is still solid & sound & looks OK.
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Pearson 26 #1200