Hex editing is a combination of knowing what you're looking for, and knowing how to change it. Here's an example from the Combat Rifle Ammo's item pickup entry.
The red section I've outlined is the item's dimensions - in this case, it's 2 grid by 1 grid. The blue section is it's stack size, and is 50 items per stack for the combat rifle ammo.
There's generally speaking two kinds of entry in a hex editing scenario - either you're changing a value (the stack size or item dimensions, in this case), or you're enabling/disabling a flag, such as whether or not an attribute is active or not. If you're changing a value, then you just need to know the hex value of your normal decimal value - say you're changing the stack size for combat rifle ammo to 500 per stack, then you need to take 500, and turn it into a hex value - the easiest way to do this is to open your trusty windows calculator, pull down the "View" menu, and switch it to programmer mode, enter 500 as your value, and hit the "Hex" radio button - this tells you that 500 in decimal is equal to 1F4 in hex.
Here comes the only tricky bit - some games have the bits switched - 1F4 on your calculator will be backwards and not enough digits for the game, so you have to "pad" the entry with extra zeroes (to make it the right number of digits), and then put it in backwards to get it read properly - first we reverse it, and type it out in batches of 2 - "F4 1", and then pad the extra zeroes "F4 01". Now you just go back to your file and replace the "32 00" to "F4 01".
The other kind of entry is a flag - and those are easy, it's just a 01 or a 00 - 1 is on, 0 is off. The only hard part for that is figuring out which of the 0's and 1's is your flag
That brings us to finding the data in the first place - for that, you mostly just have to practice, and you have to think like a program (or programmer). You'll usually find item data in one of two places - either the item has it's own file (like our combat rifle ammo example), or there's a master database with all of that information in it. Sometimes, as is the case with DX:HR, it's both - in DXHR we have our individual file entries, but they're enclosed in a container file (the pickup_database.drm file).
So far from looking at all of the pickup items, it looks like the first 255 bytes of the file are pertinent information for the item, the remainder of the file is the icon path. It's up to us to figure out what that pertinent information actually is
ammo_combatrifleAmmo.png
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