New answers tagged downgrade
Your bootloader needs to be unlocked for you to install a custom OS. Keep in mind, unlocking bootloader will most-likely void your warrenty. And I think you also will stop receiving any future OS upgrades from your manufactures/carrier.
It depends on the manufacturer and the android version most likely. When there are new system updates, there are also often new bootloader versions available. Those are automatically updated to run on the newest software and provide support for the new android version. The installation of older software packages is often restricted by the newer bootloader. ...
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