How large a scale and with how many countries participating would cloud seeding be able to reverse these effects? Last I remember it was only a few countries in Asia that were attempting anything of the sort.
Disregard the obvious environmental risks of spraying silver iodide in the air, cloud seeding will artificially redirect rainfall in specific areas, which may deprive downstream regions of water, harming biodiversity. Note that cloud seeding is currently used for drought management, not global warming mitigation.