[Suggestion] Let the configuration values in the Data Managements tab of the Process properties be an expression

Another suggestion, there's no way for these processes variables to be updated in batch?

Agreed, it would be neat to at least be able to set that value to a constant, or an expression that spits out different values per different input priority levels, PV states, etc.  I'm not 100% sure how feasible it is to implement from an Appian Engine perspective (there might be severe limitations into what data could possibly be taken into account), but that doesn't prevent it from being a significant quality-of-life issue.

For your specific case, if it's critical to bulk change in hundreds of process models at once, I'd consider perhaps editing the XML files directly in an exported application package, and re-importing.  This is an extremely unsupported method, and would need to be done very carefully, but I'd consider it worth the extra effort in exchange for saving 5 or 10 hours of manual labor.

I've always been thinking this is more of a safeguard, since changing the process model archive settings will take immediate effect on all process instances in the system for that process model, also preventing us from setting these values dynamically for different instances, with the current platform.  I learned this early on in the Portal days, where process instances in-memory were necessary for reporting.  Lowering the process model archive settings immediately archived completed process instances, removing them from those portal reports.

For "updating process variables", are you attempting to add/remove PVs in running instances or just update theri values?  For bulk updates to pv values, I've always scripted that through 1 process which loops the Set External PVs service of the Get and Set External Process Variables plugin, based on process instance IDs retrieved from queryProcessAnalytics.