What happens if selection rules change after job advertisement?

Dear Sir, The Bihar government released Advertisement No. 07/2022 for the post of ANM (10,709 posts), based on the 2018 rules where selection was through counseling on a merit basis. However, the government later changed and implemented the new 2023 rules, under which selection is done through a written examination. ANMs who were previously working on a contract basis have filed a case in the High Court (Case No. CWJC 14755).