@sana_john - You can add a classification without impacting existing classifications.
Taking the example from one of your other comments on this question, let's assume you already have "id", "name", and "category" as classifications for your Tracking Code (s.campaign / v0) report. You could add a new classification such as "sub-category" without impacting existing data and or reporting.
If you have Classification Rules running for this eVar, you can add rules to account for the new "sub-category" classification without impacting other classifications. If you're uploading a classification file (.tab), you can achieve the same result as long as you don't enter new values for the existing classifications.
@sana_john Not sure if I understood the question correctly, if you add a new campaign classification and upload data to it, it will impact retroactively as well - for historical dates too. Other reports won't be impacted if the data isn't modified or altered.