Is there a way to modify process model details? specifically created by and modified by

Check out the plug-in "republish as user", for your dev environment.  This will allow you (after doing some busy work ahead of time) to programmatically republish a list of process models under the authority of a different account (preferably a service account etc). 

For your production environment (and hopefully other environments above dev), hopefully you've already been doing automated deployments under the username of a service account, which of course completely prevents this issue in the first place.

Thanks Mike, will check out suggestion.

Yes its only an issue in DEV as deployments to higher environments use a service account.

One workaround I've also come up with, in case this helps - only something you can use in Dev environments for obvious reasons - if there is a deactivated user account that "owns" a lot of different process models and is particularly problematic, it's possible to reactivate that user, set them as an admin, rename them to something sorta generic, then add them to the service accounts group.  Being a member of the service accounts group keeps that user from being able to ever do a normal login, mitigating any extra security concerns from this approach.

This approach sounds more pragmatic. Thanks again

Thanks - and I agree; i've been using it in my dev environment to mitigate issues originally caused by the entire original dev team being deactivated, and haven't come up with any downsides yet.  Especially since we can now edit usernames.

Thanks - and I agree; i've been using it in my dev environment to mitigate issues originally caused by the entire original dev team being deactivated, and haven't come up with any downsides yet.  Especially since we can now edit usernames.