Jailbreaker will love to hear this it is possible to downgrade iOS 9 – 9.0.2 back to iOS 8.4.1 even after Apple stop signing the iOS 8.4.1 through their authentication servers. It means people who upgrade their devices to iOS 9.0.x but not feeling well with new iOS firmware then want to rollback to previous iOS 8 version, then it now possible by using a tool called OdysseusOTA 2.0. Check out more details.
OdysseusOTA is updated to version 2.0, which in fact a command line interface enable you to downgrade your own iPhone 5, iPhone 5c, iPhone 4S, iPad 3 and iPad 2 running iOS 9.0.x back to iOS 8.4.1. Even by using OdysseusOTA you can upgrade your iOS 7.x.x device to iOS 8.4.1 rather than iOS 9.
iOS 9 – 9.0.2 Downgrade Back To iOS 8.4.1 Using OdysseusOTA 2.0
You can download the new update via OTA by navigating to Settings -> General -> Software Update. If you are getting the OTA update then you can download iOS 9.0.2 IPSW files with direct download links. People who already get this new update but facing some issues and need to downgrade iOS 9.0.2 back to iOS 8.4.1 to fix the issues, then down here a very simple guide to get back the last update, as Apple has not yet blocked the signing window for this.
The developer of OdysseusOTA 2 tihmstar demonstrate how it works:
This works because apple still signs 8.4.1 OTAblobs for these devices and we have keys for them. This method does not work on any other iOS version.
A jailbreak is required for downgrading.
To downgrade iOS 9- iOS 9.0.1, iOS 9.0.2 back to iOS 8.4.1 follow this video guide how downgrade process is performed:
One thing is important here that inside the video description you can find the links to required tools and the readme.txt having list of commands to perform iOS 9.0.x downgrade back to iOS 8.4.1.