A straight forward answer to your question is No. One cannot apply for a change from an ICT to any type of visa within SA.
With regard to your second question, you need to fall within a prescribed critical skill for you to apply for a critical skills visa. Each has a professional body which is governed by. To confirm whether you qualify one may need to get an assessment of skills in conjunction with qualification.
You may need to get a professional advise a detailed case assessment. You welcome to inbox me for further particulars