new_contents: import sublime
  import sublime_plugin
  from os.path import exists, join
  
  TEMPLATE_NAME = "custom-template.html"
  
  
  def set_template():
      path = join(sublime.packages_path(), "User", TEMPLATE_NAME)
      settings = sublime.load_settings("MarkdownPreview.sublime-settings")
      if settings.get("html_template") != path:
          print("setting")
          settings.set("html_template", path)
          sublime.save_settings("MarkdownPreview.sublime-settings")
  
  
  class SetMarkdownTemplate(sublime_plugin.ApplicationCommand):
      def run(self):
          set_template()
  
  
  def plugin_loaded():
      set_template()
  
subject: Add script to set markdown template