In order to apply a modifier I understand this must happen in Obj. mode, but must I also add a separate material as to not influence the original object? That’s all for now - thanks.
if you want to keep your original obj then make a copy of it
If I make a copy of the original obj then is the modifier applied to the copy? Also when adding another mesh and while selected pressing the Y and applying a modifier like subsurf < this adds the modifier to the whole - what needs to be done to apply the modifier only to the selected obj?
To prevent confusion with the terms:
Object, object mode: different object types (mesh, curve, surface, meta, empty…), manipulating whole objects, their hierarchy, group of objects or object instances.
Mesh/curve etc, edit mode: internal structure of one object, and one object only. Depending on object type, it could have connected/unconnected structure or no structure at all. For example, a mesh object without any vertices is possible.
Adding a modifier to your object: select the object and in the properties editor, select one or more modifiers from the list.
Applying a modifier for the object: go to the modifier properties and press “apply” button on a modifier
I’m not following your questions at all but I’m going to guess that you have one mesh object that has unconnected geometry. You can select the parts you want to separate and press P -> separate by selection. That separates that piece to its own object, which has the same modifiers that the original object had.