Hi,
Thanks for using our plugins. I can help out here.
Unfortunately, for now adding functions or editing the templates is the only way to make changes to the text.
If you think that is something you would like as a feature I encourage you to visit our User Voice Page and either upvote an existing request or make a new request there.
http://tribe.uservoice.com/
For making this change the quickest way to do it is to take this template:
plugins/event-tickets-plus/src/views/wootickets/tickets.php
And following our themer’s guide:
https://theeventscalendar.com/knowledgebase/themers-guide/
Move it here:
yourtheme/tribe-events/wootickets/tickets.php
Then once in your theme you can change the word Tickets and Add to Cart what you like.
Let me know if you have any follow up questions.
Thanks