Is there any way to moddify- or create a new mesh? Not a static mesh... But an actual mesh.
Sorry for bothering everybody if you can't.
to modify static mesh (and ive never tried this) i believe you would first put a static mesh in your map, right click it, and go to convert -> to brush. then add to that brush whatever you are wanting and then right click and go to convert -> static mesh
to make static mesh its simply putting a bunch of brushes together and converting them to static mesh via that same right click menu
the best method for creating a new SM is to build it in your favourite modeling app and export it to .ASE, a file format which can be imported into UnrealEd. See the sticky in the modeling category for free tools.