You don't necessarily have to! Once the maximum number of licensed users is reached, new users will automatically disable the oldest inactive account. This frees administrators from managing the Add-on users.
What if I want to restrict which users are allowed to install the Add-on?
Yes you can. Ask your IT Administrator to login to the Google Administrator Console first. Then paste the link below for more instructions from Google:
If your administrator is not in a position to do this, do not buy a site license. Instead you have to buy individual licenses. Otherwise other users in your site/domain can take your license.
How can my users install the add-on?
They can either search for the 'Mail Merge' add-on from Google Docs Add-on->Get Add-ons... menu or you can simply give them this link to install it:
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