For my first tutorial, I will show you how to edit retired numbers. Sadly the ability to edit retired numbers was not included by mne2 in his pre-game editor, so we have to do this manually with a hexeditor.
First off, open up the retired_numbers.dat file in your database using the hex editor and here's an explanation of what means what:

To put in the correct retired number, you can't type in the number that you actually retired but rather the number in hexadecimal. To do that, you can for example use this converter. So to find what Lemieux's 66 is in hexadecimal, you type 66 into the decimal box and convert it. The hexadecimal is 42.
To find the team ID, it is easiest if a number is already retired for that team. You look for the player and you find the team ID. However if this is not case, open club.dat using your hex editor. Check the explanation below:

The team ID is only one or two hex values.
The easiest way to add retired numbers is by overwriting ones that are set for defunct teams. They are Willie O'Ree, Martin St. Amour and B.J. MacPherson (San Diego Gulls) and Nick Vitucci (Greenville Grrrowl).
To actually add more retired numbers to the file, you will have to copy the whole command for a retired number so from the number of succession to the retired number and add it to the end of the file. The hexeditor will most likely ask you if you want to increase the data file size, click yes. You will however have to edit the number of succession now and increase it by 1 each time you add a retired number.
Finally for EHM to load the larger file size, you have to open index.dat and search for retired_numbers.dat Highlighted below is the number that you have to edit:

That is the last number of succession you will find in retired_numbers.dat + 1. So if you have added 5 retired numbers to retired_numbers.dat, then you have to increase this number by 5, so from 43 01 to 48 01.
That's it. Coming up next is a tutorial on how to edit league histories.