There are two main types of fibre needles, Thorn needles and Bamboo needles. Both are basically hardened wooden needles that can be re-sharpened after playing.
Bamboo needles usually have a triangular cross-section and need a suitable hole in the sound-box to fit. These are sharpened by cutting off a slice at the end of the needle to produce a new point. Thus can be done with a craft knife but there are patent cutters available to do the job efficiently.
Please note that steel needles cannot be re-sharpened.