This is a complicated thing, but I will say it very clearly:

How can I change an object from another EP, to work without the EP.

For example:
If there's an object for The Sims 2 Nightlife, but I don't have Nightlife, how can I change this object, for it to work without Nightlife.

If there's a mod or a tutorial for that, please let me know.

Thanks

Assuming it's a regular object that does not need Nightlife stuff to function (i.e. something like a chair, not a car), you can extract the mesh, textures, descriptions, object name, price, and material definition info from the .package file, clone it properly so it require only the base game, and use all the data in your new clone package. No, there's not a tutorial to do exactly that but if you do a basic object meshing tutorial you'll see the basics.