[sublimetext2] Set default syntax to different filetype in Sublime Text 2

How do I set a default filetype for a certain file extension in Sublime Text 2? Specifically I want to have *.cfg files default to having Ini syntax highlighting but I cannot seem to figure out how I could create this custom setting.

Go to a Packages/User, create (or edit) a .sublime-settings file named after the Syntax where you want to add the extensions, Ini.sublime-settings in your case, then write there something like this:

{
    "extensions":["cfg"]
}

And then restart Sublime Text

You can turn on syntax highlighting based on the contents of the file.

For example, my Makefiles regardless of their extension the first line as follows:

#-*-Makefile-*- vim:syntax=make

This is typical practice for other editors such as vim.

However, for this to work you need to modify the Makefile.tmLanguage file.

1. Find the file (for Sublime Text 3 in Ubuntu) at:

   /opt/sublime_text/Packages/Makefile.sublime-package
   

Note, that is really a zip file. Copy it, rename with .zip at the end, and extract the Makefile.tmLanguage file from it.

2. Edit the new Makefile.tmLanguage by adding the "firstLineMatch" key and string after the "fileTypes" section. In the example below, the last two lines are new (should be added by you). The <string> section holds the regular expression, that will enable syntax highlighting for the files that match the first line. This expression recognizes two patterns: "-*-Makefile-*-" and "vim:syntax=make".

   ...
   <key>fileTypes</key>
   <array>
       <string>GNUmakefile</string>
       <string>makefile</string>
       <string>Makefile</string>
       <string>OCamlMakefile</string>
       <string>make</string>
   </array>
   
   <key>firstLineMatch</key>
   <string>^#\s*-\*-Makefile-\*-|^#.*\s*vim:syntax=make</string>
   

3. Place the modified Makefile.tmLanguage in the User settings directory:

   ~/.config/sublime-text-3/Packages/User/Makefile.tmLanguage
   

All the files matching the first line rule should turn the syntax highlighting on when opened.

In ST2 there's a package you can install called Default FileType which does just that.

More info here.