Sorry, another no. Atlassian's system does not allow more than one valid license. You can overrule an old one with a new one but never join two licenses.
But there are options to "save" users:
1. Anonymous users:
There are several options to use lesser users in Confluence. One can work with a so called "anonymous user account". Here one does not log into Confluence but will work with a standard guest user id. This "collective user" can be treated like any user, receive permissions, read, write and comment. It's just not personalized. Here all guests could comment for example. In a community wiki all anonymous guests can even change documents.
2. Shared users:
Here you can input part of your users into Confluence by using an "active-directory-group" and the other part separately and manually. These manually created users can be used by any number of users at the same time. In our wiki, for example, several employees use a user called "//SEIBERT/MEDIA-employee" in order to input not personalized content into our pages. By doing this, you can lower the total of users in the system.
If you are now asking if this "saving of users" is not against the terms or conditions of use of Atlassian:
Atlassian, of course, can allow or forbid certain practices. Right now the two above described options are technically available and Atlassian does not prohibit them. Sometimes those practices are even offered and recommended. In certain cases, we can also recommend those methods to our clients to save license cost.