Is it a workflow that is like a pre loop to what the current workflow is doing?
In that case, workflow links might be a good solution. Make it the default workflow for the category arguments and let files naturally use it as needed.
If it’s replacing a one state or super simple workflow...
Workflow links again. Push all the files from the current workflow into new one and obsolete the old one.
More than likely, it’s just a variant of the new one.
This is harder but won’t have a obsolete workflow hanging around for the life of the vault. That is to simply reconfigure the existing workflow to match the new one. It’s more challenging and needs some testing but shouldn’t be so hard as you did the heavy lifting developing the new workflow.
Whatever you do, inform and educate your user base so they can help you catch any transition ’boogers’.