Yamaha authorized showrooms and service centers are the best places to inquire about modifications and upgrades for their motorcycles. They have the expertise and access to genuine Yamaha parts. If you're interested in modifying your Yamaha YZF-R15 V3 to the YZF-R15 V4, it's recommended to visit an authorized Yamaha showroom or service center and discuss your requirements with their staff.
They will be able to provide you with accurate information regarding the feasibility, availability, cost, and compatibility of the modifications you're seeking. Keep in mind that modifying a motorcycle might have legal implications and can affect warranty coverage, so it's important to consult with the authorized dealership to ensure everything is done within the appropriate guidelines.