Yes the first Tag is the main tag for steemit and can not be changed , but all other tags can! Yes you need to use #popcontest as the first tag but this gives you plenty of time to add another positive post entry ! a good idea to do is check out past winners posts and other entries in the tag to get an idea of what to do or how they do it , and keep it as original as possible ! You have untill Sunday to enter ! 😃😃😃