Are you sure this is not hardcoded? Has someone else changed this successfully? If you look through the projectile file, an example entry:
Code:
projectile arrow_fiery
flaming arrow
effect arrows_fire_new_set
end_effect arrow_flaming_impact_ground_set
end_man_effect man_impact_tiny_set
end_package_effect arrow_flaming_impact_wall_set
end_shatter_effect arrow_flaming_impact_ground_set
end_shatter_man_effect man_impact_tiny_set
end_shatter_package_effect arrow_flaming_broken_impact_wall_set
effect_offset -0.85
damage 0
radius 0.1
mass 0.05
accuracy_vs_units 0.07
affected_by_rain
fiery
min_angle -60
max_angle 65
velocity 20 48
display aimed
effect_only
The first row seems to indicate "flaming", which is what is described in the delay section. Some others have "exploding". I couldn't find any instances of gunpowder. So my guess as to how it works is you need a based projectile, we'll call it monkey_shot. Then if you want to light it on fire, you'd have virtually the same entry as monkey_shot, with:
Code:
projectile monkey_shot_fiery
flaming monkey_shot
The other parameter being 'fiery'. I'm guessing that this is a hardcoded aspect, and it is meant to act on the disposition of a projectile as opposed to the type of projectile. So an arrow travels at X speed, and is delayed by 15.0 when it is on fire. So that area isn't describing a projectile type as much as it's describing the state a projectile is in. And with most states (think unit special abilities in the EDU), it is probably hardcoded to not accept new states.