How to manually assign bibliography numbers?

I have a list of references and citations already inserted. Regarding this list I have two questions:

  1. How can I manually specify that reference 1, 2 become 18, 13? I.e. How to change reference number for a specific citation and bibliography reference?

  2. How can I start numbering from a specific number? I.e. how to start from 42?

Thanks in advance

Why would you want to do (1)?  if you want them alphabetically, you just change the ouput style options.  if because it is coming form somewhere else, you could hide the citation, as hidden text (My preference, so I can still see it) or using the show only in bibliography option in edit citation) and type in what you want.  

  1. The option to start at any number is available on the endnote ribbon, bibliography setting menu, layout tab.