How to set species to be randomly used by AI?

It requires you to do some fine tuning of your own. Go into the steam workshop and find Stellaris and then this mod. The path should be "Steam\SteamApps\workshop\content\281990\814332008. Once there, open up the .zip file and open the common folder and then the species_classes folder. Unzip the 6 .txt files (I prefer to keep them in the same folder as the .zip file for easy management. Next, open each one in Notepad++ (Don't use textpad or notepad). Under the name of the species and above portraits (should be something like line 11) it'll have "randomized = no" Just delete that line. Save the file and put it back into the .zip, overwriting the original in there. The easiest way I've found to do that is to drag the file into the .zip while it's opened.

Removing not needed races / species

It's possible to remove (hide) the non-animated specified yourself or hide any section you don't want for example to be used by AI / spawned. Follow the same steps as before and go back to the files in common folder. All races are listed in files. Each section is defined by separate file. When you have the files you want to adjust open (remember to use notepad++, any other program doesn't work) add a "#" in front of the portraits you don't want.

Please be aware that in case of mod update is performed, it will reset your changes. So either you will need to repeat the steps or you can keep copy of files in common folder. However, be careful, if you overwrite new files, you may miss new races once they added.