If the ball bearings are not Shiny even the slightest bit dull replace them if they look shiny new leave em in unless your going on a tour.
I just finished servicing some Campagnolo hubs all shiny so back in and I always lightly foil the hubs with aluminum foil.
The Aluminum foil will show you exactly how much wear is on the cone because the race where it is worn will turn grey immediately even after a few hundred miles..
I wrap the axle in duct tape or use and old axle then put the cones on and spin while holding aluminum foil on it. it takes about 1 second to see the wear...
Then I wipe it off and either replace or reuse.
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riding