@bigsupersquid Thanks for Replying buddy! 
1) I got stock kitkat ota zip and flashed it via HBOOT (relocking bootloader, renaming that file to 0P9CIMG.zip and copying it to sd card) it'll wipe all the old data + system files + everything in the phone and install stock kitkat rom and if your bootloader got tampered, or showing security warning, it'll show "software status-official")
Then i downloaded software updates, 3-4 of them, and i've copied those zip files (before installing) for future use. Now, i'm downloading stock mm ota. i had searched whole phone for that 1GB mm zip file, even hidden files, and also by connecting phone to pc, but it isn't showing that zip.
pls tell me how could i retrieve that file.
2)Please tell me in detail, how to change the imei/meid numbers of the phone using qpst or dfs??
And if i dont change the imei/meid numbers to the original one, what would be the pros/cons for that?
Hoping for a fast reply again
as i have to install the update :fingers-crossed:
1) I got stock kitkat ota zip and flashed it via HBOOT (relocking bootloader, renaming that file to 0P9CIMG.zip and copying it to sd card) it'll wipe all the old data + system files + everything in the phone and install stock kitkat rom and if your bootloader got tampered, or showing security warning, it'll show "software status-official")
Then i downloaded software updates, 3-4 of them, and i've copied those zip files (before installing) for future use. Now, i'm downloading stock mm ota. i had searched whole phone for that 1GB mm zip file, even hidden files, and also by connecting phone to pc, but it isn't showing that zip.
pls tell me how could i retrieve that file.
2)Please tell me in detail, how to change the imei/meid numbers of the phone using qpst or dfs??
And if i dont change the imei/meid numbers to the original one, what would be the pros/cons for that?
Hoping for a fast reply again
I think you'll have to use phone service tools like qpst or dfs to change imei, dunno how that got messed up with just twrp.
For ruu try Google search "htc desire 816d a5dwg " plus your carrier to see if htc official exe is available. Think i saw the 816d mm zip floating around the 816 device forums here too but don't remember which one (general, development, q&a)
My battery charging varies.
Sometimes i have to turn it off completely to get it to charge and then it'll take overnight to do it. A bad cable or banged up micro usb port can cause problems too. I've had good luck with a micro usb magnetic cable from wish, just took a month to receive it.
If you have stock lollipop, you should be able to use it to update to stock mm... The update zip will end up in /cache rather than downloads folder.
That's about all I've got.