The process in which a relatively unspecialized cell acquires specialized features of a Malpighian tubule stellate cell. A Malpighian tubule stellate cell is a specialized epithelial secretory cell that moves chloride ions and water across the tubule epithelium. [ http://www.ncbi.nlm.nih.gov/pubmed/19783135 GOC:dph GOC:mtg_kidney_jan10 ]