Pass variables from one preprocess function to another in .theme
well after finking a lot about this problem, i realized that i don't wont to duplicate this variable at all.

lets start from beginning i wanted to copy the $variables['message_list'] from status-messages.html.twig to make my custom layout for different situation. 

for example i wanted to have different layout/design of status message on  my custom login page and another layout/design for my custom register page. but now i understend that i can have this two in one place (in status-messages.html.twig) i can check if my URL is /login tean  with help of twig if condition i can render one layout and if  my URL is /register then i could have second layout! and in aver situation u would have default layout.

is that correct? how would you solve the problem if you ware in my place