If you want to replace the FSB with another gas block, the hardest part is to drive the pins out to remove the original FSB. Make sure you can remove the muzzle device if any. The rest should not be very hard.
The pins on the front sight block of an AR-15 are tapper pins, the pins are not straight like a roll pin, use a punch no bigger than the pin and hit it with a hammer, if it doesn't move, turn it (the gas block) over.
depending on the maker, several manufactures put the pins in opposite of the rest of the makers, look at the pins to see if one side is larger than the other, Make sure you support the underside.