How do I keep a range with copy paste macro

Hello, I have a macro assigned to a button which copies a selection of rows in my excel worksheet & pastes it in the next blank row below. This macro is as follows:

Rows("18:61").Select
Selection.Copy
Selection.Insert Shift:=xlDown
Application.CutCopyMode = False

In the rows covered in the main macro above, there is another macro assigned to another button which copies & inserts a row within this main selection. This macro is as follows:

Range("Agent").Select
Selection.Copy
ActiveCell.Offset(1, 0).Select
Selection.Insert Shift:=xlDown
Application.CutCopyMode = False

When I have used the first main macro, then try to use the insert rows macro as above, the Range "Agent" only works on the second copied section as it keeps referring to the original Range that was set & therefore I cant insert rows into more than one of the main sections.

Is there a way to get the range to change when the first main macro is used e.g. give the range a new name or should i use a completely different method to get the same outcome?

Assisstance with this would be greatly appreciated.

Thanks