You can call the login method multiple times in an active session. The SDK compares the identifiers you pass against the last set it stored, and skips the request only when the two sets are exactly identical. Changing, adding, or removing any identifier makes it a different set, and a new request is sent.
The stored set is updated when the call is made, not when the response succeeds. If a login request fails, calling login again with the same identifiers has no effect; the SDK retries with the stored identifiers on the next session start.
Refer to the Android, iOS, React Native, Flutter, and Cordova pages for the login method.