If you ticked the option to 'enable recipients to forward data' on the Send page, you can (as the sender) also use this functionality to add recipients.
If you did not tick this option when the transaction was created, then it will not be possible to add new recipients / forward.
You can remove access to a transaction using the Revoke function on the Activity page.
It is possible to change (add or remove) recipients of a MX Distribution, but you would need to speak to an Administrator for your account, to see if they have Distributions as part of their package. An Administrator must also create the initial Distribution and pass control to you.
With Distributions, it is also possible to use version control and limit access to only the latest version of a particular package.
See below on how to view the full list of Administrators.