Is it a good practice to use session or local collection to change UI?

For example, in order to show/hide some divs when click, I will use session to do this.

Sometimes I will use local collection to do this. for example, I have a post page with some comments, I will store postId, showComments into local collection, and in template.onCreated i will get postId and subscribe, in template.helpers I will define showComments.

But in this case, user can easily tamper the local collection and change the webpage. Is it a good practice in terms of security and design?