All kind time of day! Tell me that I should do a mix or a modifier. Is on the site 10 links. They are different classes. You need to make them a effect on mouse hover. Now, each link to specify the opacity or make one out of the mix, and maybe a modifier to all to set opacity immediately?
To make a link class for all with a common set of parameters to it with hover opacity c, a changes all links on the site to hang on to elements such as header__link. If you want to manage via the modifier, then link_hover. Ie example class="header__link link link_hover"