I just wondering if its possible to customize the text in the featured silders? For example that I have an alternative text on the main pages slider and this text doesn’t show in the page/post the slider points to.
Yes, you can do this. You can use Excerpt field for that.
When editing your Post there is a field called Excerpt right after Post Edit Field. If you can’t see this field you can enable it via Screen Options on the upper right corner of Post Edit Page.
However, there is no Excerpt field for Pages but you can enable it via various plugins available on WordPress.org