[LG Optimus L9 P760, P765, P768, P769] Mars11_:
Ever since I bought my L9 a month ago I've been tweaking it. I've done simple things like root and overclocking/undervolting, but I've also done more complicated things like deodexing the whole ROM and swapping the internal and external SD cards.

WARNING: USE INFORMATION AND FILES AT YOUR OWN RISK. DON'T COME HERE IF YOUR PHONE IS BRICKED.YOU HAVE BEEN WARNED.

However, I will help if you're having errors or freezes because of the scripts, if you say what you've already tried. :D​

What I've Done:

Root

Deleted T-Mobile Bloatware

Overclock and undervolt at boot

Changed LCD Density

Deodexed ROM

Installed Jellybean's (4.2) keyboard

Themed the SystemUI.apk

Swap internal and external SD cards at boot

Bind Google Music library to SD card at boot

How I Did It:

Rooting:

I used Lelus method, you can find several threads detailing that.

Deleted T-Mobile Bloatware

At first I just used the built-in disable_tmous_packages.sh located in /system/etc/, but then decided to delete them.

Overclock and Undervolt

I use Tasker, but you could use numerous apps to run the script at boot (w/ root/su). My script is based off of what's detailed in this thread.

You can either download the script, or copy this:

#!/system/bin/sh
insmod /system/lib/modules/symsearch.ko
insmod /system/lib/modules/cpu_control.ko

echo 0 300 840 > /proc/cpu_control/tweak_cpu
echo 1 600 850 > /proc/cpu_control/tweak_cpu
echo 2 800 870 > /proc/cpu_control/tweak_cpu
echo 3 1200 890 > /proc/cpu_control/tweak_cpu
#echo 3 1300 890 > /proc/cpu_control/tweak_cpu

echo hotplug > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor

cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor

(The 1300 was for testing, it doesn't add any performance and going above it just cuts your MFlops by more than half.)

Change LCD Density:

This one is easy, I just lowered the density to 212 from the default so the text would be smaller and I could fit more on the screen.

Deodex ROM:

I followed the instructions on this thread to deodex, it was simple and took about 10 minutes.

Install Jellybean's (4.2) Keyboard:

I extracted the files from CM10.1 and put them on my phone, works like a charm. Downloads: Keyboard APK (Put this in /system/app/). Library 1, Library 2 (Put these in /system/lib/).

Theming SystemUI.apk

After deodexing I changed the status bar (status_bar_background2.png) and a few other images to my liking. (I used an app the first time around and it did that transparent part between each notification.)

Swapped Mounting Points Internal and External SD Cards:

I used method #3 from this thread, but it didn't work so I tweaked it into this script. I just run it at boot (w/ root/su) with Tasker.

#!/system/bin/sh

su
busybox mount -o remount,rw /

busybox mount -t vfat -o umask=0000 /dev/block/vold/179:61 /mnt/sdcard
#busybox mount -t exfat -o umask=0000 /dev/block/vold/179:61 /mnt/sdcard
if busybox mount | busybox grep vold/179:61; then
busybox mount -o bind /data/media /mnt/sdcard/external_sd
chmod 0777 /sdcard/external_sd
fi

Used bind to get Google Play Music Library on SD Card:

Google Play Music stores the offline and cached mp3s in /data/data/com.google.android.music/ (Which is the same partition as the internal SD card BTW.) I made a little script that runs at boot (w/ root/su) with Tasker. With this you have to make a directory named MusicCache on your SD card.

mount -o bind /mnt/sdcard/MusicCache/ /data/data/com.google.android.music/

Q and A:

Q:"Is this (the overclock/undervolt script) optimized for performance or battery life?"

A: Not to brag, but mine does both.

Q:"What happens to existing apps installed in the internal SD card?"

A: I recommend coping everything to the external SD before swapping, then nothing happens.

Q:"After we swap, is the internal SD card rendered useless?"

A: Nope, the internal SD is accessible from the /mnt/sdcard/external_sd/. (I might mess with the script later to mount to /sdcard/internal_sd)

Q:I want to mess with the overclock/undervolt script, how is it formatted?

A: echo line# cpufreq voltage > /proc/cpu_control/tweak_cpu

Q:Can I use the bind with another application?

A: Sure! Just switch around the directories.

Images!

Note: I will be adding more as I tweak more things.