Texture Atlas

That is not precisely animation, so sorry if the section is wrong...
ok my problem is that i have an atlas with the sprite i need in my animations, but every time i modify the atlas to add something, unity lose ALL the information i gave to the atlas, so i have to re-cut it with sprite editor.
Also, there is always something wrog after that, for example a certain sprite is moved after another one i recently added, so i have to chang ein the game everything related to the old sprite because it's been moved (i know i explained bad, sorry)

do you know a solution to this? or an alternative way, just a method that can allow me to add sprite to the atlas in order, without modifying the old ones