I'm using Joomla 1.7 and k2 2.5 component
I'd like to duplicate the categories and items tabs so I can have some tabs like this:
items | categories | branches | companies
So will work branches as items and compianies as categories
What wold be the best way?
For now Im duplicating all files and changing the source.
The only way you are going to be able to do the tabs like that is to hack the K2 core code, which is a bad idea. You could see just companies/branches by filtering by category in the items manager.
If you really need to have separate tabs for those pieces of content, you might look at Yootheme's Zoo. That would allow you to have a Companies and Branches tab without hacking anything.