[Android Software/Hacking General [Developers Only]] alexceltare2:
On that note, here are the features that you're most likely going to tweak. Others include fixes and critical radio (RIL) components that I wouldn't recommend changing unless necessary. Change the values if is already in the list or add them if missing. Duplicates or conflicts may cause problems.

Enable VoLTE support

(not recommended if your phone does not support IMS/4G, customer.xml also needs updating)

<CscFeature_IMS_EnableIMS>TRUE</CscFeature_IMS_EnableIMS>
<CscFeature_IMS_EnableVoLTE>TRUE</CscFeature_IMS_EnableVoLTE>
<CscFeature_RIL_ConfigAlwaysOnApn>bip,ims,xcap</CscFeature_RIL_ConfigAlwaysOnApn>
<CscFeature_RIL_SupportVolte>TRUE</CscFeature_RIL_SupportVolte>
<CscFeature_RIL_SetVolteAudioPath>TRUE</CscFeature_RIL_SetVolteAudioPath>
<CscFeature_RIL_WbamrDefaultOn>TRUE</CscFeature_RIL_WbamrDefaultOn>
<CscFeature_Setting_ConfigVolteSettingMenu>TRUE</CscFeature_Setting_ConfigVolteSettingMenu>
<!--DO NOT ENABLE THE FOLLOWING FEATURE IF USING A DUAL-SIM PHONE OR YOU MAY ENCOUNTER CRASHES-->
<CscFeature_Common_AutoConfigurationType>NO_DFLT_CSC,SIMBASED_OMC</CscFeature_Common_AutoConfigurationType>

Remove/Add the NFC enabled icon in the status bar + Card mode

(can be "DEFAULT" for phone icon, "ATT" for standard logo, "Cityzi" for France NFC or "NONE" for no icon)

<CscFeature_NFC_StatusBarIconType>DEFAULT</CscFeature_NFC_StatusBarIconType>
<CscFeature_NFC_SupportReaderModeApi>TRUE</CscFeature_NFC_SupportReaderModeApi>
<CscFeature_NFC_ConfigAdvancedSettings>Enable</CscFeature_NFC_ConfigAdvancedSettings>
<CscFeature_NFC_ConfigCardmodeRoutingTypeForHce>ROUTE_ON_WHEN_SCREEN_ON</CscFeature_NFC_ConfigCardmodeRoutingTypeForHce>

Enable shutter sound switch in camera settings

(insure /system/csc/customer.xml doesn't block this feature)

<CscFeature_Camera_ShutterSoundMenu>TRUE</CscFeature_Camera_ShutterSoundMenu>

Enable native voice call recording

(+icon showing which call has been recorded)

<CscFeature_VoiceCall_ConfigRecording>RecordingAllowed</CscFeature_VoiceCall_ConfigRecording>
<CscFeature_Contact_EnableLogIconForVoiceRecord>TRUE</CscFeature_Contact_EnableLogIconForVoiceRecord>

Enable Wi-Fi calling in phone settings

(not recommended if your phone does not support ePDG subsystem)

<CscFeature_Setting_SupportWifiCall>TRUE</CscFeature_Setting_SupportWifiCall>
<CscFeature_Setting_SupportWifiCallingMenu>TRUE</CscFeature_Setting_SupportWifiCallingMenu>
<CscFeature_RIL_SupportWifiCalling>TRUE</CscFeature_RIL_SupportWifiCalling>
<CscFeature_RIL_SupportEpdg>TRUE</CscFeature_RIL_SupportEpdg>

Enable Auto Power On/Off Menu in Clock app

(not available in Android 7.0+)

<CscFeature_Clock_EnableAutoPowerOnOffMenu>TRUE</CscFeature_Clock_EnableAutoPowerOnOffMenu>

Enable Option to Schedule Message Sending

<CscFeature_Message_EnableScheduledMessage>TRUE</CscFeature_Message_EnableScheduledMessage>
<CscFeature_Message_EnableScheduledMsgBox>TRUE</CscFeature_Message_EnableScheduledMsgBox>

Disable Anti-Malware Feature in Smart Manager Program

<CscFeature_SmartManager_DisableAntiMalware>TRUE</CscFeature_SmartManager_DisableAntiMalware>

Enable "Floating or Air Messages" Feature

(requires applet preinstalled)

<CscFeature_Common_EnableAirMessage>TRUE</CscFeature_Common_EnableAirMessage>

Enable "Call/Message Block" Feature

<CscFeature_Setting_EnableMenuBlockCallMsg>TRUE</CscFeature_Setting_EnableMenuBlockCallMsg>

Add "Call" Icon in Call Logs List for Direct Calling

<CscFeature_Contact_EnableCallButtonInList>TRUE</CscFeature_Contact_EnableCallButtonInList>

All quick settings toggles

(add only the ones needed, remove the brackets "()" as they're only for explanation, the slash "/" denotes a duplicate toggle so choose only one of it)

<CscFeature_SystemUI_ConfigDefQuickSettingItem>Wifi,SilentMode(Speaker),MobileData,Bluetooth,RotationLock,Flashlight,AirplaneMode,ScreenCapture,AdaptiveDisplay,Nfc,WifiHotspot,BlueLightFilter,PowerSaving,Aod/SmartView,Location,Sync,VoLte,DormantMode/Dnd,TouchSensitivity,WifiCalling,PersonalMode(PrivateMode),AllShareCast,QuickConnect,DeviceVisibility(PhoneVisibility),SFinder,Ebook(ReadingMode),FloatingMessage,SideKey,SecureFolder,Dolby,UHQ(UltraHighQualityUpscaller),RedPacket,CarMode,BikeMode,DesktopMode,KidsHome,ToddlerMode,SmartStay,SmartPause,SmartScroll,AirGesture,AirView,Toolbox,DailyBoard,EdgeLighting,SpenRemote,MultiWindow,UltraPowerSaving,PowerPlanning,Performance(PerformanceMode),UDS/UltraDataSaving,DataSaving,NetworkBooster</CscFeature_SystemUI_ConfigDefQuickSettingItem>

Enable 5Ghz & WiFi Extender option for the WiFi hotspot

<CscFeature_Wifi_SupportMobileAp5G>TRUE</CscFeature_Wifi_SupportMobileAp5G>
<CscFeature_Wifi_SupportMobileApWifiExtender>TRUE</CscFeature_Wifi_SupportMobileApWifiExtender>

Support all DLNA Protocols

(Can be NONE, DMC_ONLY or ALL)

<CscFeature_Common_SupportDLNA>ALL</CscFeature_Common_SupportDLNA>

Enable power OFF additional information and force restart

<CscFeature_Framework_SupportForceRestartGlobalAction>TRUE</CscFeature_Framework_SupportForceRestartGlobalAction>

Disable the Weather feature in Clock app

<CscFeature_Clock_DisableAccWeatherInfo>TRUE</CscFeature_Clock_DisableAccWeatherInfo>

Combine First Name and Last Name in Contacts in just one field

<CscFeature_Contact_UseUniNameField>TRUE</CscFeature_Contact_UseUniNameField>

Support for Auto-Rotate and Hide folders in Gallery app

<CscFeature_Gallery_AddAutoRotationIcon>TRUE</CscFeature_Gallery_AddAutoRotationIcon>
<CscFeature_Gallery_SupportHideAlbum>TRUE</CscFeature_Gallery_SupportHideAlbum>

Hide/Show certain UI Elements

(Yellow Pages in Contacts, Net speed and roaming in Quick Settings & HW Version in About screen)

<CscFeature_Contact_ConfigForYellowPage>HIDE</CscFeature_Contact_ConfigForYellowPage>
<CscFeature_SystemUI_SupportDataUsageViewOnQuickPanel>FALSE</CscFeature_SystemUI_SupportDataUsageViewOnQuickPanel>
<CscFeature_Setting_EnableDataRoamingButtonInQuickPanel>TRUE</CscFeature_Setting_EnableDataRoamingButtonInQuickPanel>
<CscFeature_Setting_EnableHwVersionDisplay>TRUE</CscFeature_Setting_EnableHwVersionDisplay>

Display all possible languages & Countries

(Israel & Taiwan)

<CscFeature_Framework_DisableShowAllLanguages>FALSE</CscFeature_Framework_DisableShowAllLanguages>
<CscFeature_Setting_DisableIsraelCountry>FALSE</CscFeature_Setting_DisableIsraelCountry>
<CscFeature_Clock_ReplaceNameTaiwanWithTaipei>FALSE</CscFeature_Clock_ReplaceNameTaiwanWithTaipei>

Enable Advanced WiFi menu & Auto-Connect during sleep

<CscFeature_Wifi_SupportAdvancedMenu>TRUE</CscFeature_Wifi_SupportAdvancedMenu>
<CscFeature_Wifi_SupportAutoReconnect>TRUE</CscFeature_Wifi_SupportAutoReconnect>

Enable/Disable Geographical location description on voice calls

(CSC dependant)

<CscFeature_VoiceCall_DisableGeoDescription>FALSE</CscFeature_VoiceCall_DisableGeoDescription>

Correct camera flicker

(AC mains standard freq. region dependant)

<CscFeature_Camera_CameraFlicker>50hz</CscFeature_Camera_CameraFlicker>

Enable/Disable popup notification when turning on Mobile Data

("<your csc>" for always show and "" for always hide)

<CscFeature_SystemUI_ConfigQuickSettingPopup></CscFeature_SystemUI_ConfigQuickSettingPopup>

Fix caller number-contact information matching when receiving a call

(ID matching is usually 11 digits for China, 9 digits for rest of the world )

<CscFeature_Contact_EnableDynCallerIdMatchingDigitWithAutoSim>TRUE</CscFeature_Contact_EnableDynCallerIdMatchingDigitWithAutoSim>
<CscFeature_RIL_CallerIdMatchingDigit>9</CscFeature_RIL_CallerIdMatchingDigit>