DISCLAIMER: PGI has said that ANY sort of game modifications are against the rules, but me and many other people play with game modifications, such as sound, HUD and other visual mods so I don't think they will, or can do anything about it. Either way, use at your discretion. All my modifications work in online play, these have been tested both in private lobbies and quick play matches.

What the files do:

-zMechs.pak

    Edits many mechs, but not all so they don't have Jump Jet screen shake. Now you can shoot while jumping up!
    Currently supports the following mechs: Cicada M/3F, NSR(Clan), Highlander(All non-special variants), Highlander IIC(All non-special variants), Shadow Hawk IIC(all variants), Spider 5K, Urbanmech IS (All non-special Variants), Vapor Eagle 1/2/3, Victor 9A1
    If you want a specific mech to have no screen shake, you can either request it here or edit it yourself (see: instructions)


-zWeapons.pak

    Multiple weapon edits.
    RAC 2 & 5 no longer have a ramp-up time, you can start shooting immediately.
    Gauss rifles charge up instantly, you can shoot immediately by simply pressing your fire button and releasing, don't have to hold the button down.
    Ultra Autocannons and other ballistics with Burst-fire capabilities, like clan autocannons fire their bursts faster. Ultra autocannons can also double tap faster.
    HAG 20,30,40 fire their burst faster.


Installation:

zMechs.pak: Extract to \MechWarrior Online\Game\mechs
zWeapons.pak: Extract to \MechWarrior Online\Game

KEEP THE FILES NAMED AS IS

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Making your own edits:
Before doing anything, you will need at least 7zip to be able to extract files from the games .pak files. The ready to go PowerShell scripts also require 7zip.I've provided some tools to make your own edits to the game (File: mwo_xml_edits.7z), if you wish to do so. There's a couple PowerShell scripts which create a package for you to use, and the file structure you should be following when you create your own mech or weapon edits.
Be very careful of typos, because these cause the .xml file to not parse, and the modification will not work!
Some edits work in online play, and some don't. The edits in the ready to go modifications are confirmed to work online, but feel free to experiment on other things if you wish.

Weapon editing:

You will need a copy of Weapons.xml file to make changes. I've provided an outdated example file inside the file structure, YOU MUST REPLACE THIS WITH YOUR OWN AS IT IS OUTDATED. To get your own, you need to go to \MechWarrior Online\Game\ and open GameData.pak in 7z. Inside GameData.pak you can find Weapons.xml in \Libs\Items\Weapons\. Copy (or extract) and replace the old Weapons.xml located in \mwo_xml_edits\GameData\Libs\Items with the new one. Some edits don't work in online play, but some do. If you wish to edit a property (for example the screen shake that Heavy Gauss causes), open Weapons.xml file in your favourite text editor and search for the weapon and its properties you wish to change. In my example with the Heavy Gauss and its screenshake, I would ctrl+f for HeavyGauss(not case-sensitive) and look for the property that matches what I want. In this case, it would probably be called "WeaponShakeIntensity".

When you're done, right click "compress_equipment.ps1" and select "Run with PowerShell" to make a .pak ready for the game in the correct format. Drag the new .pak file in to \MechWarrior Online\Game.

Mech editing:

The mechs folder has a few example mechs and folders there ready to go. THESE ARE ALSO OUTDATED, so it is recommended to replace them with your own references before making edits. Similar to weapon editing, you can find the reference files in \MechWarrior Online\Game\mechs, but this time they're already sorted, so you can select the mech you like and grab its required files. For example, if I wanted to edit an Arctic Cheetah or any of its variants, I would open arcticcheetah.pak with 7z and go to \Objects\mechs\arcticcheetah\, and extract the necessary files from there. Note that these files are .mdf files instead of .xml files, but the editing process is similar. The file structure demands that each .mdf file is under their proper mech folder, so for each mech you will have to make their own folder if you wish to edit them. You don't have to edit all of them, just the ones you want to modify.

Now, if for example I would want to edit Jump Jet screen shake away from Arctic Cheetah A, I would make a folder in \mwo_xml_edits\mechs\Objects\mechs\ that is called "arcticcheetah"(multiple .mdf files can be in the same folder, as long as they belong to the chassis itself, as they are variants of the chassis), and inside there I would copy & paste ach-a.mdf for editing. After that is done, I open the new file with my favourite text editing tool, and search for the property I need. I want to remove Jump Jet shake, so the property matching this would be called "ShakeDamping". I ctrl+f search for this property, and change its value to 1. For reference: 1 in this case means no shake and 0 means there is infinity shake and your game will probably crash from doing so.

When you're done, right click "compress_mechs.ps1" and select "Run with PowerShell" to make a .pak ready for the game in the correct
format. Drag the new .pak file in to \MechWarrior Online\Game\mechs.