Install old Cumulative Update SQL Server 2016 Standard

We were running on SQL Server 2016 Standard Edition 2016 SP2-CU4 on our ALWAYS-ON HA cluster. Due to some recent issues one of our nodes got corrupted and we had to replace it with a new node. Since this was a fresh image from AWS Marketplace it came with SP2-CU13 (latest) out of the box. The client wants this to be rolled-back to the original SP2-CU4 (no plans/requirement of upgrading to CU13). As a primary step I tried to install the SP2-CU4 KB article on the instance but that does not work with the attached error message. (No SQL Server instance or feature can be updated on this computer) Q1 - How can SP2-CU4 installed on the server. Q2 - What is the impact if the cluster runs on different CU's.