You'll need to do the following.
1- Export your workflow.
2- Make the follwoing changes to the workflow in the customizations.xml file.
a- Change the workflow name and all references to the old name.
b- Change the value in the EntityDependency Tag.
3- Ensure that the original workflow is not published before you import the new workflow.
NOTE: I've only done this for workflows that do not have lots of references to the EntityDependency. e.g. if you export a sales process that references opportunity and try to run it for an account it would not work and you will get warning messages.
Give the above a try and tune according to your requirements. Make sure you try this in a test environment and not the live server.
H.