As per the FX3APIGuide, there are two types of interrupts:
The high priority (non pre-emptable interrupts) are:
DMA interrupt for USB sockets
DMA interrupt for GPIF sockets
DMA interrupt for Serial peripheral sockets
The low priority (pre-emptable interrupts) are: System control interrupt (used for suspend/wakeup)
OS scheduler interrupt (timer based)
Some interrupts in the FX3 system need to be prioritized over others to ensure that the application can meet all the USB spec
requirements and transfer rates. In particular, the USB core interrupt must be handled at the highest priority , and all the DMA interrupts should be allotted the next high priority level.
So, it not advisable to change the priority of these interrupts.
Also, CyU3PVicIntSetPriority() function is not used in the library and is not expected to be called