How to Customize iOS 5 Notification Center Background on iPhone 4?

Hello Alex, I am not sure regarding widgets or tweaks in Cydia that will allow you to change the background of the Notification Center. But the good news is, you will be able to change the background of your Notification Center manually and set your favourite wallpaper as Notification Center background. The wallpaper should be sized as 640 by 960 pixels. You can check Google Images to pick up one. Anyway, you can follow the tutorial posted below on how to customize Notification Center background:

Step 1: Jailbreak iPhone, iPad, and iPod Touch on iOS 5 using Redsn0w 0.9.9b7.
Step 2: Download WinSCP for Windows or Cyberduck for Mac OS X.
Step 3: Launch Cydia on the Springboard of your jailbroken iPhone and install OpenSSH on your iOS device.
Step 4: Once completely installed, access your network connection and get your IP address.
Step 5: Now launch WinSCP if you are on Windows or Cyberduck if you were using a Mac and then enter the following information:

Host name:
Username: root (default iOS username)
Password: alpine (default iOS password)

Step 6: Using the SSH client, navigate to the following directory:

System/Library/CoreServices/Sprinboard.app

Step 7: Then scroll down and look for an image named BulletinListLinen.png or BulletinListLinen@2x.png Notification Center image. And then replace it with your preferred background image. (Note: You should name the image just like the one found in the directory)
Step 8: Now go to the following directory:

private/var/mobile/Library/Caches

Step 9: Then look for a file called: com.apple.SpringBoard.notificationCenterLinen and then delete it.

That’s it! Just simply tethered boot your device and you are good to go!