It is great to see so many projects moving to git and GitHub in particular. GitHub is incredibly helpful for quickly taking a look at a project and figuring out what areas of a project are still evolving and being actively developed.
If you want to change the title, edit/delete comments, close the PR, assign a person or labels then you'll need the proper permissions.
If you want to make changes to the code you'll need to have push access to the same repo (which is usually the case if you're on the same team because then you don't need to use forks). Otherwise you can always amend the commit(s) before merging them into master.