I dont care what you want to call dispersing chemical agents in to the atmosphere. Its dispersing chemical agents in to the atmosphere. Seeding clouds, would that not be modifying weather with a chemical agent. No consent from the population to be doing so. I'm afraid that constitutes an act of terrorism as deemed by the 1978 UN treaty on weather modification.
Water vapor is a chemical agent that is created when hydrocarbons are burned. Therefore, any airplane that burns hydrocarbons (aka, fuel) is seeding clouds, modifying the weather and engaging in terrorism. Also, by your definition, anyone who heats their house with gas, oil or wood is creating water vapor (as well as poisonous CO
2 gas) that gets into the atmosphere, seeds clouds, modifies the weather and is therefore engaging in an act of terrorism. Don't forget cars, factories, trees, animals and just about anything else that generates water vapor.
There are plenty of natural and man made chemicals that get into the atmosphere and modify the weather. Why bother with chemtrails?