tfs - Using features (portfolio backlog) after finished in agile -

in case have feature completed , after time, there's new requirement add value feature, use same feature or new 1 ?

example:

feature: user registration  user stories: visitor want able register web site. visitor want able register web site using facebook. visitor want able register web site using twitter. registered user want able connect account facebook. registered user want able connect account twitter. registered user want able create username , password login. 

after stories gets implemented, , feature completed, 1 month later, have new requirement registration process. (increasing security, or add additional social login, whatever)

should add them finished feature "user registration" or best create new one?

i'm using tfs scrum , feature terminology, applies process template

you create new one.

features , pbi's time limited placeholders desired functionality. 1 done, done. i'd have new functionality not captured , implemented during life of feature or pbi need new 1 prioritised product owner.