Durability is handled by the 
	
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, specifically 
	
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, and set from the weapon note tags.
As in 
$[0].note inside 
www/data/GameLanguage2/Weapons.json or in whatever language you are using.
There are a number of properties (Durability, Durability Variance, Durability Maximum, Bypass Durability, Unbreakable, etc), which are all completely documented inside 
www/js/plugins/YEP_ItemCore.js.
If you just want to make all items unbreakable, you can just edit the code in 
YEP_X_ItemDurability.js to set 
obj.durability = -1; after the end of the 
for (var i = 0; i < notedata.length; i++) { block. It's easier than to add <Unbreakable> to every weapon.
They're not going to show up in the usual cheat tools because those are completely new properties added by a third-party plugin (like most things in this game), and not simple RPGM switches or variables.
EDIT:
Some other code tips and cheats:
QJ-MPMZLib-imoutoUtil.js contains most of the game-specific code. This file contains methods called by the game events, 
and is 3434 lines long.
The auto-update code lives aither in 
QJ-MPMZLib-imoutoUtil.js or in 
QJ-MPMZLib-AnsuzEffects.js, calling e.g. 
https://script.google.com/macros/s/AKfycbyAOCAFafhItnPc_l_gJk0i6nCPqUTPP-RuSESS4ATr3IDmmJMS63DBOcXIbA_JTzOO/exec?mode=LatestVersion&lang=en&version=75 to get the latest version number.
The update files are public. The auto-update code just pulls the various directories (containing only changed files) from 
	
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 on GitHub. So if you want to know if there's an update, you can literally check there.
Instantly level up heart level:
In 
js/plugins/QJ-MPMZLib-imoutoUtil.js, inside 
_imoutoUtilKoukanLevelChange,
Under 
let hearts = $gameVariables.value(15);,
Insert 
$gameVariables.setValue(17, 100 * (hearts + 1));.