The option to Notify providers from the Jobs View allows selecting an email template, however, it does not let you edit the chosen template (unlike the Notify providers option from the Project page).
It is not possible to notify providers assigned to jobs in different projects at once. You select the job from its corresponding Project page and click on Tools > Email... > choose Email template and edit it, but it is necessary to repeat this action for every different project.
After you select an email template to notify providers from the Jobs View, the email body should be displayed in a pop-up window to allow you to edit it (like it happens in the Project page when choosing an email template to notify providers).
A PM can easily notify providers assigned to jobs from multiple projects and add to the email template any instruction required for those specific jobs.