Add the following ammunition, compatible with any arrow-thrower (bows, crossbolters of either type):
Injection Arrow Level 1 Price 66 Cartridges 20 Bulk L Injection, Critical Injection DC + 2 or Corrode <Acid Damage>
These arrows can be filled with any liquid, which they release upon impact. The internal reservoir is lined with a plastic polymer which is hardness 5, so anything corrosive, such as acid, put inside, which can deal more than 5 damage will rapidly dissolve the lining (treat as having 1 hp). The critical effect is "added" to the weapon like a fusion's would be, meaning you have to choose between them without a special rule, such as the devastating fusion, saying otherwise.
Darts use the same rules of being Hardness 5, HP 1 for being filled with acid, as well as the generic rules for supplying their thrower with the relevant critical effects for both types of chemicals.
For both ammunition types, because no two liquid chemicals are identical densities, and modern weapons are extraordinarily sensitive to density, as their weapon-feed mechanisms are designed to work in both zero-g and high or very high gravitic conditions, attempting to fire an automatic weapon with ammunition of more than 1 chemical (e.g. a 20-arrow weapon with 10 acid arrows and 10 healing serum arrows) automatically jams the weapon, firing only 1 round. The weapon must be reloaded to clear the jam.
Basic weapons-grade acid can be bought with the following profile per "dose" (enough to fill the reservoir of 1 dart or arrow):
Weapons-grade Acid Level 2 Price 6 Charges 1 Bulk - Special Damage 1d4 A
Move Needler Pistols to Projectile.
For each Projectile Small Arm is that is not the Needler Pistol and shoots rounds, add the option to pay 40% of the small arm's cost (rounding up to the nearest multiple of 5) to convert it to a type of Needler Pistol. This multiplies the capacity by 2/3 (taking the capacity to 10, for the Paragon), changes the ammo type to dart, and downgrades the damage from Xd6 to Xd4.
Move Needler Rifles to Projectile.
For each Projectile Longarm is that is not the Needler Rifle and shoots rounds, add the option to pay 45% of the longarm's cost (rounding up to the nearest multiple of 5) to convert it to a type of Needler Rifle. This multiplies the capacity by 2, changes the ammo type to dart, multiplies the range increment by 2/3 (rounding down to the nearest multiple of 5), and downgrades the damage from Xd8 to Xd6.