Mass update to subscribers/membership

Hi

When I extend a membership it is not reflected in the subscribers, to avoid manually going in and changing all the subscribers can you implement a mass change to end dates of a membership for all subscribers please ?

I have 1 membership defined with 100 subscribers and do not want the subscribers to renew themselves, I would like to renew it for them, instead of going into 100 subscribers and adding in a new membership, can I just change the end date of the 1 main membership ? or if it needs to be a new membership, how do I easily add 100 subscribers to a new membership ?

thank you
paul