It sounds like you want to import a schema that has the same username as the database you are importing to. Easiest way to do this is to create another user in the second database, with the same grants as the first. Then run imp using the <b>FROMUSER=originaluser TOUSER=newuser</b> arguments. You don’t want to run a full import because then it will try to recreate the data files and reload catalog information. If you have multiple users you want to import, you will have to repeat the above process for each schema.
This means tables already exists with the same name, if you want to insert tables which already exist then u can use ignore=y option in import it will check if table already exist it wont return error, instead it will append.
Hope this helps