1) You could do that, but the moment you flash an OTA from the March to June update, you run the real, very high risk of a hard brick (because of the mismatch between the bootloader, GPT and the rest of the system). Given clever_idiot's bootloader is downgraded, OTAs are generally a very risky idea, hence the idea of using the fastboot ROM to repair and flash a clean copy of both the GPT/bootloader. Of course, without knowing what stock build of 7.0 was on the device before, flashing the wrong fastboot Nougat ROM might itself invite a brick...@echo92 is it suggestable to flash March's security patch, not complete, but only system/boot and required one only ?
So other stuffs will not be touched ?
Or
as he can boot into bootloader, if he get succeed to install TWRP, then he can flash custom ROM.
@clever_idiot let echo92 confirm above things.
2)It might be safest, if in fastboot we can boot into TWRP (which TWRP are you using btw, clever_idiot?), then we might be able to flash a custom ROM, without having to worry about the bootloader/GPT and flash a custom logo.bin to hide the bootloader warning. That is, assuming the rest of the device firmware is okay, which is difficult to determine at the moment without a booting device.