LED Backlight driver output current
The SC4509 feedback pin requires 0.2 volts across it to set the LED current. The current that flows thru the LEDs also flow thru a resistor (R1) that sets the 0.2 volts depending on the current flow.



You say your design needs 40mA and this is well within the limits for the device so, alter the resistor value to set 40mA instead of 30mA.


  So is it correct assumption that the IC can be used in this design
  since the total power remain with in the limit?


No, this is not correct. If R1 has a value that produces 30mA then it will produce 30mA and not 40mA. It's a constant current device not a constant power device.