A code that begins with the GS digits 50 is a patch code. These codes only work for GameShark versions 2.2 and up. This code shortens a string of consecutive codes down to two codes. For this kind of code to be used you must have a string of at least 2 codes that begin with the GS digits 80 or 30. And they all have to have a consecutive pattern to the code. In example the code should look like this before the patch code:

Example code only
80067780 FFFF
80067782 FFFF
80067784 FFFF
80067786 FFFF

It should not look like this:

80067780 FFFF
80067784 FFFF
80067786 FFFF
8006778A FFFF

Notice that the last digit in the main part of the code does not change by the same amount from one code to the next to the next. They all have to be the same distance apart.

This is how the code from the first example would look with a patch code.

50000402 0000
80067780 FFFF

And without the patch code

80067780 FFFF
80067782 FFFF
80067784 FFFF
80067786 FFFF

THE BREAK DOWN

Now the breakdown of this code is relatively simple.
This is how it works:
The patch code begins with 5000 these digits just tell your GS that you are using the patch code.
The 5th & 6th digits of the code are 04. This tells the GS how many codes are in the string. In this case we are going to shorten a 4 code string.
The 7th & 8th digits in the code are 02. These digits tell your GS how much the codes increase by to get to the next code in the string. In this case the codes are all 2 digits apart from the last.
The last four digits of the code are set to 0000. This means that the quantity digits do not change from what they are in the first code which is FFFF.

So this is what it look like broken down:
5000 04 02 0000

You can also use this patch code to increase the quantity digits on a consecutive string of codes. To do this all you would have to do is make the code the same way as the last example was made. Then decide the amount you want the codes quantity digits to increase by. So you would change the last four digits in the code to accompany that amount.