Question Ascend P6-U06 KitKat Rooting & Headphone volume

First of all, good day for Everyone!

So i got a little problem here. Short story of my phone:
I bought a Huawei Ascend P6-U06 from Hungarian Telekom (formerly T-Mobile). It had some problem (even the
service center couldn't tell what was it), so i returned it, and they sent back an unlocked one, so
actually i have an original, unlocked Ascend P6-U06, for about half a year (I asked Telekom about this,
and they said that they can't do nothing about this, if it's unlocked, than it's unlocked, end).

I think everybody know, that this phone isn't the loudest one, if we talking about listening to music on
headset/earphone, whatever. This problem could be eliminated, if the phone is rooted, that's OK.
Everything worked like a charm on 4.2.2, rooted, and made the phone louder, by the "workaround" i learned
in this site. (Great thanks for this, to you, XDA =))

The problem is, i can't root the phone, since 4.4.2 (B510). None of the known methods worked for me (no
eRoot, no Root Wizard, no blabla, i tried all of these, even towelroot). After this, i wanted to try out
some custom ROM stuff, but because i couldn't find a complete, step-by-step guide about how to completely
backup my entire system, install e.g. TWRP, and return to my original (keeping the warranty), if
something's gone wrong, i decided not to do this. I only found posts saying "do a nandroid backup"...
Really? Okay, but how? And "now install TWRP"... So i gave up.

I tried to modify an original ROM provided by "huaweinews", and i found a software called "Huawei Update
Extractor", and it sounded great, because it could unpack, sign, and repack the firmware, so i thought
i'll just unpack, modify the "local.prop" (?) file in it, the program will sign it, repack, and show must
go on. Aha... The program unpacked .img files for me, witch couldn't be opened in Windows. I found
some "ext4 to ext2" or whatever stuff, but it couldn't repack files to a proper .img file, and the guy
who made the thread, said "make an updatable zip". Again... How? There no freakin step-by-step guide
about this.

The only thing i have to do, is to put 2 doublecrosses (or hashtags), into the local.prop (?) file
cust/channel/neeurope/prop), before the 2 lines, and i don't really care how it can be done, e.g. by some
magic rooting stuff, or modifying the ROM and installing it.

I'd like to ask whether it's possible, to do a little modification like this to a Stock ROM, and flash it
like Stock? Because that would be the best for me.
Many thanks in advance,
Phone data:
Huawei Ascend P6-U06, Android 4.4.2 EMUI 2.3 B510 (from
Baseband - IMC1202_PENTA
Kernel - 3.0.8-00787-g55ab691
Build - P6-U06V100R001C00B510
Custom - CUSTC185D510

p.s.: I'm sorry for the long post, i just wanted to make everything clear