Historically, tools like PwnageTool or Sn0wbreeze allowed users to create custom IPSW files that included Cydia and a jailbreak out of the box.
There are several reasons why users may want to modify an IPSW file: modify ipsw file
Every official IPSW file is cryptographically signed by Apple. During a restore operation, iTunes or Finder contacts Apple's servers to verify the signature. If the file has been modified, the signature check fails and the restore is rejected. This is why many custom IPSW workflows require bootrom exploits (like checkm8 or limera1n) that allow you to bypass signature checks by putting the device into a special "pwned DFU" state before restoring. If the file has been modified, the signature
: Researchers often modify the filesystem to inject binaries or bypass security checks. Tools like Tools like While you can edit the files
While you can edit the files inside, installing the "custom" version on a device is the real hurdle: Signature Verification: iTunes and the device's hardware (BootROM) check for a digital signature