This is a tutorial for Huawei users. After, a deelaw complained he couldn't change the imei of his smartphone, I managed to comb this up for him. And of course, other kins sharing his plight.
For reasons best known to Huawei, their device doesn't support changing of imei with MTK Engineering Mode

You can Download MTK engineering mode start - mtk engineering mode start_1.1.apk

Note: your phone must be rooted.
Learn how to Root with the below links

How To Root Android Phones (All Methods)

learn How to Root Any Android Phone With KingRoot apk.

Which Huawei phones will this work on? 

The method has tested and confirmed working fine with Huawei Y600-U20, Huawei Y5, Y3, Huawei G750 (honor 3x and 3C), Huawei MediaPad T1.7.0 (Tablet).
Note that the method also works for other MTK devices that are difficult to change it's IMEI through MTK Engineering Mode.

How To Change Your Huawei Smartphone IMEI with Chamelephon apk

In this method, we are going to use an application called Chameleon.

Simply follow the steps carefully. No need of CDS information or engineering mode at all.

Steps to change Huawei imei 

1. Download and install Chamelephon.apk on your android phone

2. Open Chamelephon and grant it superuser access permission that's root access to your device.

3. The first box is for the IMEI of the sim 1, if you are using a dual sim phone. And the second box for Sim 2.

4. Input the IMEI number you wish to change to in any of the boxes. Simply leave any of the boxes you did not wish to change as the way you met it.

5. Then click Apply New IMEIs.

6. A popup box will ask “Do you confirm changing the IMEIs?” Click on Change button.

7. Close everything and restart your phone or put it in Airplane mode for 5 seconds before you back it to normal mode, then dial *#06# to view your new IMEIs.

All things being equal, it should be changed to the new one by now and if so, you've just changed the imei of your stubborn Huawei device.