If I create an opener can I re-use it in my other videos?

The opener is an end product but can that generated opener video then be included as part of the videos I create? In other words I create the opener and then use the created video as a clip at the beginner of my other videos not changing anything at all from the opener I initially created? Kind of like an opener to a tv show (but for youtube).

Probably no, as the opener is the end-product and can be used only one project, you will need to get a new license to use it on multiple videos

So to give an example let’s say I create an opener for someone can they not then use that video at the start of whatever they want or do they then need to go to Envato and buy a license every time they use the opener I created from them using the template I purchased on Envato?

The item you have purchased is only for one end-product ( one item )
If you use it multiple projects, you may need either extended license ( if available and the terms allows it ) or you’d need to get the item purchased whenever it’s used.

Which item exactly you’ve purchased? From Elements? From Marketplace?

I haven’t yet purchased it. I’m trying to decide if it’s better to go with a custom item or buy one from the marketplace. It would be an opener to a series of tutorial videos. I’m basically trying to have a one time fee rather than having to pay a fee for every tutorial video I create (both the opener and music). Some are just going to be 10’ish minutes but some will be as short as a minute or two. And making a series of tutorials can quickly add up and I then have to evaluate the value of each tutorial due to their costs to see if it’s worth it which is detrimental to my goal. Especially if I want to do a large number of small tutorials…