I am using Raspbian Buster.Assume I have added kali-linux repositories in my source list. y question is , 1.What are the risks of adding two different repositories in one OS? 2.Is it going to corrupt my OS or software? 3.How to maintain more than one repositories?
A Debian repository is mainly made for a specific distribution and even for a specific version of it. For Raspbian/Debian you will find different repositories e.g. for version Jessie (or old-old-stable), Stretch (or old-stable) , Buster (or stable) and so on. The packages in the repository are pre compiled for the version and the installable executable programs fit optimal into its environment. This way you can just
sudo apt install myprogram without the need to compile it. The disadvantage is that this pre compiled programs only fit to the distribution they are compiled for. You can add for example the repository for kali-linux to
/etc/apt/sources.list and you should also be able to update the package lists with
sudo apt update. Afterwards you will find the packages for kali-linux in addition to the packages for Raspbian with
apt list. But if you install a package for kali-linux (as far as
apt doesn't complain dependency errors) and try to run it, it will often crash with segmentation fault because kernel, modules and libraries from Raspbian doesn't fit.
You can find specific repositories which are explicitly made to run on different distributions. They are smaller and mostly support only one application, maybe with optional packages and plugins. But they have to be labeled that they are independent from a distribution so you can use it.