How to back up my current android ID? I want to flash a new rom, but it will change my android ID. Is there any way to just back up my current android ID WITHOUT make a whole-system-backup?
IF you simply backup an Apk application, from within TiB, and then restore that app, you probably WILL have problems, for such system apks on some devices (certainly, that's my experience on Lollipop for several devices lately). 
Instead, use the built in function to restore the DeviceID from another Nandroid-style backup, or when it prompts you during the startup wizard -> avoid restoring entire system apks, even within the same ROM, for the same device, and save major version of android (if this doesn't apply to you, consider yourself the lucky and rare).
There is an ALTERNATIVE TO TiB, which doesn't require a purchase, (scroll down to the most recent download attachment) here: http://forum.xda-developers.com/showthread.php?t=2109484 or be generous and support the DEV via the Play Store (search for apps/details id=com.liamw.root.androididchanger)


NOTE: The above app needs to be a system app, which is why it needs root.

You can have more than one device ID, for example, when a device has multiple users (available on certain devices running Android 4.2 or higher), in which each user appears as a completely separate device, so the ANDROID_ID value is unique to each user.
In most cases, if you can't gain root on your device (and workaround locked bootloaders, which are often the case), then you probably shouldn't be messing with DeviceID.  Walk before run, is a better slogan than "if you aren't an expert" -> because EVERYBODY at some point was clueless what they were doing.  Just climb the smaller hill first.  
For a highly relevant XDA Discussion on restoring ONLY the ID, or other stuff too, look under (google this..) nexus-4/general/titanium-backup-android-device-id-t2006461
NOTE: Above thread regards restoring lots of crazy stuff (no longer doable on most modern devices), or just the ID itself (which may be ok in many cases, STILL).
Document Your DeviceID (don't just back it up): Search for Play Store App id=com.evozi.deviceid, which can be used to document the ID via text, for your own records (along with IMEI, Mac, etc, a good first step with new devices, BEFORE you root).




ANDROID_ID (String) Official Definition from Google: 

A 64-bit number (as a hex string) that is randomly generated when the user first sets up the device and should remain constant for the lifetime of the user's device. 


GoogleSearch for this Info, via Domain: developer.android.com Under > reference > android > provider > Settings.Secure.html   ...
Which reveals this ID is a string, found in the: android.provider.Settings.NameValueTable
One of the values in: android.provider.Settings.Secure
Java Class Object: Settings.Secure (public static final class / extends Settings.NameValueTable)
NOTE on CLASS: Secure system settings, contain system preferences that applications can read but are not allowed to write. These are for preferences that the user must explicitly modify through the system UI or specialized APIs for those values, not modified directly by applications.  




How to Verify the Device_ID from TiB via 2ndary Source:


The ID provided by the play store app by evozi (that's not me, btw, and I don't know that DEV), you will find MATCHES the value in the DB for DeviceInfo backed up by TiB, which I often move to SDext2
So, use something like aSQLiteManager, go to the Database: /path.you.set.in.TiB.prefs/com.keramidas.TitaniumBackup/settings/databases-sysinfo
Then look at the Table: deviceInfo for the Field:  androidid:xxxxxxxxxxxxxxxxxxxxx




How To Backup Restore And Changing Your Android-ID With Titanium Backup

From a webpage named: "how-to-backup-restore-and-changing-your-android-id-with-titanium-backup"


Some applications or games use it as a identification ID for your account. As an example, all games from Gamevil will save your Android ID in their game archives. When you try to hack one of their games, your Android ID will get banned. And you wouldn’t be able to play their game anymore from your Android device.
To be able to play Gamevil games again, you will need a new Android ID. As far as I know, Titanium Backup is the only application in the store that have the function to changing, backup, and restore your Android ID.
Changing your Android ID is a good way to experiment with some hacks before you use it in your game data. And it is the only solution when you get banned by Gamevil.


BACKUP


Run Titanium Backup
Click on "Backup/Restore" tab
Find "Setting Storage" from the list.
Try to use the "Filters" if you have a long list of apps.
Click on "Setting Storage", and choose "Backup !"
After the Backup process, click again "Setting Storage" to open the "Backup properties"
Click the title part of your new backup (area between the Restore and Delete button)
Scroll down untill you find "Protect this backup" and click it
Now your Android ID is protected and will not get overwritten when you make another backup of your new Android ID. So you can have multiple Android ID as much as you want


CHANGE


Run your Titanium Backup
Press the menu button, click on More, and choose Manage Android ID …
TB will show you a dialog window with your current Android ID as the title
To change your Android ID, click "Create new (random) Android ID"
TB will showing your new Android ID and asking your permission to reboot the device.
Click "Yes, do it" to change your current Android ID with the new one you see on the screen.
Your device will be rebooted and have a new Android ID


RESTORE


Run your Titanium Backup
Press the menu button, click on More, and choose Manage Android ID …
TB will show you a dialog window with your current Android ID as the title
Click on "Restore Android ID from a backup"
TB will show you a list of all Android ID you have.
Click on any Android ID you want
TB will showing your new Android ID and asking your permission to reboot the device.
Click "Yes, do it" to change your current Android ID with the new one you see on the screen.
Your device will be rebooted and after the reboot your Android ID will be restored.