Successful unlock without messing up IMEI number
I did just like the OP stated and, it messed up my IMEI number. Glad I had a backup of the file.
So I went back into the HEX editor (I used HxD editor) and looked where I did the the change and noticed to the right side there were a series of numbers that started at row 41460 and ended on row 41470.
It was an 8 digit series started with 75 ending in 13, something like this 75382313. I was sure it had something to do with the unlock code but, didn't have a different SIM to check.
I sold the phone and, the guy said he had to get it unlocked so he could use it with O2 network (I think).
I text him later that day to ask if he got the phone unlocked, he said no, the place wanted $45 to SIM unlock it.
I told him to try the number listed above and it "SIM UNLOCKED" the phone. He called me back and thanked me many times for saving him $45.
Hope this helps someone else and not mess with the IMEI number!!!!