So I open your SM library.  I select a part (line), copy, close the library, open my own, and past that line in.  Then I take that component's dimensions and modify to suit a different manufacturer.  I change the name, data sheet link etc., etc.  Then I hit 'OK', and then I save the library.

If I look at something else in that library or at another library and come back to that same line, the changes I thought I entered are not there.

What are the exact steps to copy, edit and save the modified copy to another library?  I assumed build will come later when I have made all the changes I want so that I do not have to do them a part at a time for my target tools. 

Its these real elementary videos that are missing.

1. Open part in Calculator
2. Change dimensions
3. In the Library Manager (FPX), select the Gray Box to the left of the Footprint Name to highlight the entire row
4. Select the Import Part icon in the toolbar
5. A dialog box will appear and ask you if you want to update existing library part
6. Select "Yes" and the program will update all the component dimensions for the new part

So to move the part to MY fpx as desired, first I copy and paste the part to my library.  Then go through the above steps to edit and import it.

Copy, edit and import it first to my fpx, ....then save my fpx.