Yes, if you find the stock firmware backup. But many unlock firmwares prevent downgrading.
The ZLT P28 may have different hardware revisions (v1, v2, etc.). Flashing firmware intended for a different hardware revision can corrupt the bootloader, leaving the device unable to boot. Recovery often requires JTAG hardware hacking, which is beyond the skill set of average users. zlt p28 router unlock firmware download
Date: October 26, 2023 Subject: Technical Overview of ZLT P28 Architecture, Unlocking Mechanisms, and Firmware Management Yes, if you find the stock firmware backup