Reason i ask is my old vauxhall had one and if you didnt put the pin in it will fire on you, just wondered if the fabia has the same.

All Fabias have pretensioning seat belts as far as I know.

So is there anything i need to do before unbolting it from the chassis?

there is no need to do anything when removing the seat from the car , just undo the 4 spline/12 point bolts holding it down , the pretensioner is in the seat belt unit in the b-pillar , unlike other cars, notably Fords, who have the pretensioner on the seat belt buckle and the battery should be disconnected to remove the seats from them