Sounds like you are wanting to edit an EXISTING Source Template, correct?
Build/Templates/Source In the Existing Source Types list, double click on the Source type you want to edit. Click the SHORT Footnote button (I know, but this will get you to the Long Compoents 1-8, from what I understand) Edit the Footnote Text using the text codes displayed in the window. Select a style code for each code. Choose OK.