[Needed Help] Global Stable to Global beta with locked bootloader

I want to unlock my phone, I had unlock permission also but unlocking is not possible in Global Stable
I want to flash Global Beta 6.5.30 from Global stable 7.3.5.0 with locked bootloader.
Is it possible to do this with updater app & flash recovery rom of 6.5.30 & then unlocked bootloader ??

THanks

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