Absolutely! 

1. Go to evenium.com
2. Click on My Events
3. Click the name of the event under the I Organize section
4. Click on Configuration on the purple bar
5. Click Invitations & Emails
6. Click Edit invitations & emails
7. On the next page, you'll see under the Message section on the top left a New message link. 
8. Click on it and create your own custom template and send it to your participants!