Looks like "Invite Users" is handled by a plugin, and therefore can't be customized the way "Create Users" can.
BTW, if you're happy with using "Create Users" but don't understand Velocity Macro files (I don't!), you can customize part of the email by editing the "template.jira.user.created.intro" property in the following file (and then restarting JIRA):
Hey Community mates! Claire here from the Software Product Marketing team. We all know software development changes rapidly, and it's often tough to keep up. But from our research, we've found the h...
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