Not because of tensile strength or because the part is weak or that it is single use item, just that it is often rusty and crackered.
If yours is fine, there is no reason not to re-use. Mine are being replaced as they are rusty, 30 years old and ... i attacked them with the angle grinder!
I just saw that you are very experienced in the Mini world and know a lot more than me ..
Cheers for that.
Mate, I might have a few more years of dirty hands than some, but every day is a school day as they say.
I'm in Australia and thankfully, we don't get the same rust & corrosion as our UK counterparts, eg, replacing a rear subframe to us is almost unheard of, but almost seems a routine thing in the UK every 4 - 5 years.
With these particular Pins, I don't recall pulling any that were terribly rusty, though I usually do clean them up and send them out for plating. Obviously a different story in the UK.