Before starting, if you haven't already, make a profile in game otherwise this guide won't work. You need to have at least one custom profile. Be sure to select the profile before completing the next step.

Here is the link to the original guide again: https://forums.bohemia.net/forums/topic/74086-unlocking-weapons-in-armory-what-for/?do=findComment&comment=1667335

What you need to do is to first complete at least one armory mission in Arma 2 or the expansion of your choice. All you need to do is one challenge. You can start a challenge by picking a weapon in the armory screen, click try and spawn in, then wait for the game to give you a mission (should take only a few seconds.) After completing the mission, save and close the game.

Now, head to /Documents/ArmA II in your file browser and look for the profile file for Arma II ex:

"(profilename).ArmA2Profile"

Obviously, the Profile name in () refers to ur profile name in game. If you want all armory items unlocked for an expansion, look for the profile file with the expansion name in it. For example, for Operation Arrowhead, it would be: "(profilename).ArmA2OAProfile"
Open the profile file with a text editor, I used notepad. Find the line that says "armoryPoints=..." and change the number to 50000 then save the file.

NOTE: You will not have the armory points line in your profile file unless you have earned some. You can add this line to the file refer to the original guide in the link I provided for more info. I'd recommend just completing one challenge as it won't take you as long and is less confusing to do.

After allat, you should be good to go. I haven't tested this on any of the expansions, only the main game. TCEd also mentions that you should add a line if modifying an expansion profile. Refer to the link above for more info. I would assume that you wouldn't need to add the armory points line in an expansion profile if you have already earned armory points.

If you have any questions, feel free to comment them. Please note that I am not an experienced Arma player and do not know much about the game, so I may not be able to help with every issue.