nRF24L01+PA+LNA with Arduino Mega ADK

I have “special pins” stating MISO,MOSI,SCK (in the place of pins 50,51,52 on a conventional Mega- “53 is SS but is not required for the nRF”) on my Arduino Mega ADK. Can I connect the nRF24 modules’ same pins to the pins I mentioned before? If I can do I need to write codes for those pins too??

You should not need to re-write any code. Your Mega is using the same pins for the SPI bus as any other Mega, it is just the labeling of these pins that is different eg. "MISO" instead of "50". You can also use the ICSP header without making any changes to your code.

Ok so can I power it Directly from the 3.3V bus??

If you only need 150mA of supply current.
May want to add additional capacitance to the 3.3V line for power supply buffering also.

Some videos in YouTube suggested regulating 5V to 3.3V using an LM1117 voltage regulator. Is it necessary??

Okay how much current is reqd. for the module? How much current does the 3.3V Bus provide??