Your conclusion regarding that treaty is still faulty, as has already been pointed out.
You say it is faulty. I say there is plenty of evidence of weather modification going back decades.
Have any countries signed a zombie treaty? Or any other (thus far) fictional scenario requiring contingency planning?
No? Of course not. Technology which is available, at the time, is what they hope to prevent misuse of.
LOGIC says it's faulty, as well as DuckDodgers. It just doesn't logically follow, so why would you even want to draw that conclusion?
Point out the logical error.
One problem I can see is affirming the consequent.
1. Chemtrails cause geoengineering
2. Geoengineering exists.
3. Therefore chemtrails exist.
However geoengineering doesn't necessarily involve chemtrails so your reasoning isn't valid.
It's like saying
1. Rain will cause the street to get wet.
2. The street is wet
3. Therefore it's raining
Streets can get wet from things like floods and overenthusiastic lawn sprinkling.
Also, you haven't even shown that chemtrails can cause geoengineering, because nobody has ever shown that chemtrails are anything other than just normal contrails.