You can remove the afterburners by changing removing these lines in the [lights] section of the aircraft.cfg :

light.7 = 8,  -56.00,  -1.75,   0.00, cs18_ab,
light.8 = 9,  -56.00,   1.75,   0.00, cs18_ab,

I'm not sure how you will replace them. But my guess is that they are all .fx files so whatever you choose should be fine.

Mark