Re the thread title … “Try”?
There is no “try” in eventing. One must commit to “do”. :winkgrin:
It’s good you’ve already XC schooled, and you should continue to do that and feel confident about whatever level you enter. I recommend setting an example of a healthy respect for the sport, and not being too casual about it with your students and clients, as it does have a greater risk potential that what you’ve probably already been doing. It can be done safely of course, but must be done safely, if that makes sense. I say this only because your first post seems a bit indefinite and airy. Go and be fully there as an eventer-for-a-day, and not just a toe-dipper, if that makes any sense. :yes:
Get some local pointers about good starter courses, and also the courses that aren’t the best choice for a first-timer. I know that in this area there are venues that are notoriously maxed at the lower levels (think championship courses), whereas other venues are more basic and straightforward.
It would be best to go with some experienced eventers who are willing to take you under their wing and make sure you are ticking all the boxes, just as bornfree describes above. Dressage whip length, timeframes, etc. People who will check you out before and after you get on the horse and remove the illegal things and make sure you have what’s required. (like the safety armband). All that good stuff. 
Have fun! Report back how the day went!
And again when you decide to become a full-time eventer! 