For manually triggering the renumeration atleast 1mS delay is required. This can be given by EZUSB_Delay(1). As you might know, the number in the paranthesis is in terms of millisec.
However there is a function impleemnted in EZUSB library for renumeration to occur. That is EZUSB_Discon. The delay implemented in this function between connect and disconnect is 1500 millisec i.e EZUSB_Delay(1500). You can call this function directly or it is recommended to give that delay even though it works even for 1mS.