Hi @Parag Gajare,
Welcome to Atlassian Community!
In order to change the workflow for one project without affecting other projects you have to also create a new workflow schema that the project should use. It sounds like that is what you missing since all your other projects also see the new workflow.
Have a look at this overview, Project screens, schemes and fields, it will show you how all the different schemas connects to each other.
Also note that statuses are global for your instance, so if you rename a status it will affect all workflows that is using that status.
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