Not all inhabitants of the Gilead System live within the Imperium's control; xenos species are not restricted by the bureaucracy and legislation which permeates Imperial space, and often have more freedom when customising their vehicles. Agents outside the Imperium's influence have two options for customising vehicles;
Do It Yourself: This requires a Tech Test with DN equal to the combined Rarity modifiers of the Vehicle and the Wargear being installed
Requisitioning Assistance: You may attempt to requisition aid from experts, who typically have their own workshop and resources - the way you go about this is dependent on the species, as described below. You must also be in a position to access these experts, such as having access to your own void-craft or being present on the same world as them.
Aeldari Agents with access to the Craftworld of Ul-Khari may attempt to Requisition the services of a Bonesinger to customise vehicles with the AELDARI Keyword (Church of Steel, pg. 58). You must make an Influence Test with DN equal to the combined Value and Rarity of the Wargear you wish to install; this process takes 2d3 + 1 days, as the Bonesinger first completes their existing projects.
If attempting to increase an Attribute, the DN of the Influence Test is equal to twice the Rarity of the vehicle.
Drukhari crafters are usually unwilling to help others without the promise of reward. You must first find a crafter willing to carry out the job, requiring a Cunning Test with DN equal to the combined Value and Rarity of the Wargear you wish to have installed (or twice the Rarity of the vehicle if attempting to increase an Attribute); regardless of the result of this Test, you do not fail, and every Icon you roll reduces the DN of the Test by 1. If you roll a Complication on the Test, the DN is increased by 3, and you must make a DN 1 Corruption Test. If attempting to find a crafter operating outside of Comorragh, the DN is increased by 5.
When the DN reaches 0, the process is complete, and you have found a crafter to undertake the job - for a price. You must then pay Wealth equal to 1 + the Rarity modifier of the Wargear you wish to install (or 1 + the Rarity of the vehicle if attempting to increase an Attribute).
Mekboys delight in creating ever more deadly weapons of war, and can be persuaded to install Wargear or upgrade your vehicle. This requires either an Influence Test with DN equal to the combined Value and Rarity of the Wargear you wish to install or payment of Wealth equal to the Rarity of the Wargear; if attempting to increase an Attribute, the DN of the Influence Test is equal to twice the Rarity of the vehicle, or Wealth equivalent to its Rarity.
T'au society is separated into a rigid caste system, with most of the technical and engineering jobs being completed by the Earth Caste. If you wish to install Wargear on a vehicle with the T'AU Keyword, you must make an Influence Test with DN equal to the combined Value and Rarity of the Wargear you wish to install; if attempting to increase an Attribute, the DN of the Influence Test is equal to twice the Rarity of the vehicle. The DN is reduced by 1 if you are part of the T'au Faction, as the work is completed as part of the Greater Good.
Earth Caste engineers in the Gilead System have also become adept at handling common Imperial vehicles; they can install Wargear onto vehicles with the IMPERIUM Keyword, provided both the Wargear and vehicle have a Rarity of Rare or lower.