No it doesn't need to be modified after the purchase. As per CRA - Van – 20% of the amount paid for a van that has been previously adapted, (which is your case since you purchased it already wheelchair accessible) or is adapted within six months after the van was bought (minus the cost of adapting the van), to transport a person who needs to use a wheelchair, to a limit of $5,000 (for residents of Ontario, the provincial limit is $7,033).