Nope, for Kenney Studio NXT you won't be able to create anything custom this way - just through the application itself.
Viewing post in How to create template files (0.51, not NXT)
Just to be clear; There are two things here:
1. In Kenney Studio NXT a 'template' is a file created by users, it contains various elements positioned, scale, rotated and changed.
2. An element is an object from one of the included collections.
Templates can be saved/loaded from within NXT, collections have to be made using Adobe Animate.