What is the best practice for setting up and updating a column(field) in a List in a template that has been used already?

Question:

If I create a Template for Sites containing -->List-->Field1,Field2,Field3,Field4,Field5

As time goes by I have say 100 sites ...and We decide to add another Field to the list --> Field6

Is there a easy way to maintain this? 

Do i need to go to each site to add the additional field?

What is the best practice for setting up and updating a column(field) in a List in a template that has been used already?