I'm migrating from the test environment to the live environment, both of which have a separate set of users/logins/privileges.
How do I not overwrite this information when migrating from one site to another?
Assuming that you are using the Backup and Migrate module (as per your title), just use the feature to exclude selected tables, similar to what is described in the answer to the question about "Backup and Migrate exclusion recommendations?", which states:
I have following tables to exclude data (not to exclude the table altogether):
- all cache_* tables
Usually search_index saves a lot of database size.
You may also want to look at these issues:
How to backup and migrate just the user accounts?: even though it's the opposite of what your question is about, it does provide some interesting background info about this topic, i.e (quote from it):
The exclude table features are there because not all db data needs to be backed up (cache tables, search index, etc) and not all tables in a db are necessarily drupal tables (you might have wordpress installed in the same db and not want to back up those tables). You'll notice that there is no option to backup just part of a table. There is no way to backup all users with uid > x for example.
Default tables/data to exclude, which includes an interesting list of tables to not be migrated (pick what fits for you), i.e. (quote from it):
When creating a backup profile, the module by default sets the following tables to have their data excluded according to issue #209647: Exclude advice:
Entire site backup excludes default/settings.php file: just be aware that that is how it works (to avoid surprises after restore).
If you want to move user data from a Drupal site to another, you need to use the Migrate module. The Backup and migrate module is for exporting and restoring database and files.