Manually Adjust Membership Length

Hello,
Long time user here.
I sell a subscription of “3 events” but the timeframe can vary. Sometimes it is 3 weeks, sometimes the events are spread over 5 weeks etc.
When someone signs up for a membership the option is for 3 weeks which puts the end date 21 days from the start as you would expect.
So sometimes I have to manually change the end date to match our upcoming events. When I do this is re-sends the member an automated “Activate Subscription Email” email which looks unprofessional and causes confusion.

How can I manually change the subscription end date without sending an automated email?

Thanks.