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Shouldn't have to change any fuses or relays. The alternator provides the power and the only relay that is not protected by a fuse or fusible link (depends on model year) is the start solenoid on the passenger inner fender. Everything else is downstream of the alternator and fuses and wire are already sized to handle the loads that already exist on them.
The 3G swap is a very common swap and a little research (search) here will yield tons of info on the procedure.
With that said, if you plan on adding more circuits or higher amperage devices, make certain you run new wires and fuses for them. "Piggybacking" new devices onto existing circuits is a recipe for disaster.
I highly recommend this guy for a High output altenator, he has all the proper wiring as well for great prices and is proven hardware on FSB RJM Injection Tech — Welcome