If you want something installed in a kali ISO is it actually installed or just in the repo?

So for instance when you download the kali iso from the website and install it, you update the OS and upgrade it as well usually, and usually theres like 500 packages that need to be upgraded. Well lets say I want to create my own ISO. However, I want certain things installed on it, other then just some custom scripts. Will say OpenVAS for an example. So if I download and install OpenVAS, will it already be installed after I create the ISO? And by already installed, I mean that it is fully installed and I will not have to run any update or upgrade function after booting the iso to use it? I might be confused about how this works, but if that was not clear enough about what I am talking about, I mean that it (OpenVAS) is not just going to be pointed to a link of where the OS once booted can get the program in the repo?:)