How to have a dynamics number of actors in isaacgym?

I wonder if I can change the number of actors during the simulation. For example, is there any way to hide one of my actors(make it invisible)?
I find that in the document there is a saying that “There are ways to “fake” having a dynamic number of actors in an environment, which will be discussed in another section.” But I didn’t find how to do this.
Thanks in advance