Functions in trans to edit the amino acid from incorrectly charged Cys-tRNA(Pro) via a Cys-tRNA(Pro) deacylase activity. Reaction mechanism involves exclusion of catalytic water from the active site and substrate-mediated catalysis: the sulfhydryl side chain of the Cys substrate acts as a nucleophile and attacks the carbonyl center of the ester bond, leading to the cleavage of the Cys-tRNA ester bond and formation of a cyclic cysteine thiolactone intermediate. In contrast, the INS editing domain of ProRS catalyzes Ala-tRNA(Pro) hydrolysis via nucleophilic attack by a catalytic water molecule (By similarity). Belongs to the prolyl-tRNA editing family. YbaK/EbsC subfamily.