However, I've read this thread http://forum.xda-developers.com/show....php?t=2335582 which seems to confirm that the flash wont be ruined in Android 4.1.2 (I have 4.3), but when I asked the guy who flashed my phone about flashing a custom rom he said this
"He: any questions for me?
Me: yes, If I flash a custom rom..will that break the flash?
He: yes, custom roms will 100% break the flash
they flash a custom radio usually or do NVM folder wipe
so all flash settings get wiped
there are some roms that don't have radio in them
but it's risky unless you know 100% from the ROM dev that NVM folder is not being wiped
the other issue is most custom roms don't have DIAG mode
so you can't flash inside them
only touchwiz based roms have DM mode which is requiref for flashing"
How much of this is correct?, can I flash any rom, yes or no?