This script requires GTALua. 
You can download it here: http://www.gtalua.com/

Description 
This script will allow you to lock your wanted level, 
there is already one of this sort of script on but its very lacking, 
if you press U on your keyboard with this mod it opens a menu 
where you can choose on what star you want to lock it to. 

Controls 
U -- Open menu 
Numpad 5 -- Select option 
Numpad 8 -- Up 
Numpad 2 -- Down 
Back button -- Close menu 

Installation guide 
Put the folder: Lock Wanted Level into your GTALua/Addons folder
and put 8V.SFV in your main gta v directory root folder
then start the game and press U.