Can NuGet edit a config file or only add to it?

I've been working on a NuGet package for my company and one of the requirements is being able to update some of our config files.

I know it's possible to add to a config file, but is it possible to edit one?

Example:

<add name="conn" connectionString="Data Source=.\;Initial Catalog=DB;Integrated Security=True" />

changes to below

<add name="conn" connectionString="Data Source=.\;Initial Catalog=DB;User ID=ex;Password=example" />