Disable "http://connectivitycheck.gstatic.com/generate_204" check send out after each IP change.
settings put global captive_portal_detection_enabled 0
reboot is required for activating. State can be checked with
settings get global captive_portal_detection_enabled
Attention always make backup for possible recovery bevore any of this tips.
Even if they are tested.
Tested on Google Nexus 5 (Hammerhead) ; Android 4.4.4

Update Nexus 5 with Stock Rom 6.0.1 m4b30x, TWRP 3.0.2and SuperSU 2.68

# Download Image from Nexus Images
set VA="m4b30x"
set VH="10cfaa5c"
set VB="hhz20h"				--------------------------------
set VR="m8974a-2.0.50.2.30"		----- NEU
wget https://dl.google.com/dl/android/aosp/hammerhead-%VA%-factory-%VH%.tgz
gunzip hammerhead-%VA%-factory-%VH%.tgz
tar xf hammerhead-%VA%-factory-%VH%.tar
rm hammerhead-%VA%-factory-%VH%.tar
cd "hammerhead-%VA%"
unzip image-hammerhead-%VA%.zip
rm image-hammerhead-%VA%.zip
adb reboot bootloader
fastboot flash bootloader bootloader-hammerhead-%VB%.img
fastboot reboot-bootloader
fastboot flash radio radio-hammerhead-%VR%.img
fastboot reboot-bootloader
fastboot flash system system.img
fastboot flash boot boot.img
fastboot flash cache cache.img
fastboot flash recovery ../twrp-3.0.2-0-hammerhead.img
# reboot into recovery and "Advanced"->"Sideload"
# adb sideload BETA-SuperSU-v2.68-20160228150503.zip
adb sideload ../SuperSU-v2.76-20160630161323.zip
# Reboot without install TWRP SU; Login via adb sheel
su
mount -o remount,rw /system
cp /sdcard/hosts /etc/hosts
for A in 5073cd83.0  b34ac79c.0  b6ac64a1.0 ; do
  cp /sdcard/$A /system/etc/security/cacerts/
  chmod 644     /system/etc/security/cacerts/$A
done
reboot

Application can not find External SD Card

INFO: Application has WRITE_EXTERNAL_STORAGE
Problem: Application require since new Android WRITE_MEDIA_STORAGE
Fix: Allow Applications with WRITE_EXTERNAL_STORAGE also access to external media.
  su
  mount -o remount,rw /system
  vi /system/etc/permissions/platform.xml
  # Add  to the permission WRITE_EXTERNAL_STORAGE.
  mount -o remount,ro /system

Update Nexus 5 with Stock Rom 4.* and TWRP

adb reboot bootloader

# Install Xposed Xposed APK XPrivacy for better control
adb install de.robv.android.xposed.installer_*.apk
# Refresh busybox

Enable Multiuser on cell phone

su
mount -o remount,rw /system
vi /system/build.prop
# Add these two lines
lockscreen.rot_override=true
fw.max_users=4
mount -o remount,ro /system

Android System CA's

openssl x509 -inform PEM -subject_hash_old \
  -in root.crt | head -1
  
cat root.crt > a92f6437.0
openssl x509 -inform PEM -text -in root.crt \
 -out /dev/null >> a92f6437.0
adb push a92f6437.0 /sdcard/a92f6437.0
adb shell
su
mount -o remount,rw /system
cp /sdcard/a92f6437.0 /system/etc/security/cacerts/a92f6437.0
chmod 644             /system/etc/security/cacerts/a92f6437.0
reboot

ADB Terminal Width

export COLUMNS=160

No Shutter Sound

adb pull /system/app/GoogleCamera.apk
# remove OGG+WAV from apk with 7zip.
adb push GoogleCamera.apk /sdcard/
adb shell
su
mount -o remount,rw /system
cp /sdcard/GoogleCamera.apk /system/app/GoogleCamera.apk
chmod 644 /system/app/GoogleCamera.apk
reboot