i never use pencil lol, even for diagrams, filling in the blanks, crosswords, etc. hehe
i strongly think that you should use pen. if your writing is THAT messy, the markers at the centre will call in your class teacher to read it, (after all, she/he has marked your essays for 2 years, so they should know how to) my history teacher told me this, so don't worry too much about it.
i highly doubt they would have allowed you to use a laptop for this. the key reason is because people normally type faster than they write, and there is nothing wrong with your hands (e.g. if you have a broken right arm and you are right-handed, you should be entitled to one) the only excuse you have is you have messy handwriting. goodness, everyone in the state can say that too and be entitled to a laptop. i guess you'll just have to deal?
special provisions is only for seriously important cases- theres something happening at home, you're too sick to come (in that case a bos staff member must take the test to your home so you can do it), your in hospital, a friend died and you are grieving, my example earlier about breaking an arm, etc. i highly doubt that messy handwriting would have gotten you a laptop, so i'm not surprised.
anyway, i hope my somewhat long reply helped.