there are mixed views on this. but the most important thing is simply the size of the new V old rim. unless the new rim has the some measurement as the old one you simply can't reuse the spokes.
now some would say to never reuse spokes but I simply go on a case by case basis. if the wheel is a few years old and has alot of miles you should replace the spokes rather than subject them to the stress of rebuilding the wheel.
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk