To add a rule, you have to edit the style with stylish and change or add your filter.

If you want to "block" a user, edit the style and change in the line

.stream > div.tt-a[username="Chikukko"],

Chikukko to another username (without ~ or * ) or copy and create more lines:

.stream > div.tt-a[username="user1"],
.stream > div.tt-a[username="user2"],

For categorys, enter them without spaces and in small letters.