It seems, I somewhere met the third-party application of management of Workflows (of course not free).
If I find the reference - I will report in addition. It is possible to eat such opportunity there.
But the simple solution of this question cannot be.
For this purpose it is enough to glance in SQL base - (dbo.Workflows; dbo.Transitions; dbo.Status....).
Besides, there are connected documents, notifications, tasks, etc.
At the same time there is an opportunity to copy Statuses and Transitions from one Workflow to another.
And everything is farther manually.
But it needs to be done very carefully and it is desirable not in the course of work of users.
I had an idea to try option of temporary moving of all documents to mirror Workflow (for what to configure the necessary transitions) and then to return them to Initial Workflow.
But I for tests have no time.
No, you cannot overwrite workflow. Importing workflows will create copies (n).
This is a limitation, described in S-038857
HI Jaymin, Martin is correct, you cannot overwrite a workflow.