Imagine a nation state started doing this. Lets imagine the Netherlands because they realise that it is worth it for them alone when so much of their land is at sea level. They hope to reduce worldwide temps by 1.75C (to pre industrial levels) within a year or so, which would immediately halt sea level rise.

I think other nations will demand they stop - with threats of sanctions - simply because there are other nations who now depend on the higher temperatures and increased agricultural output.

Conversely, imagine a nation state like India that will experience mass death events if heat/humidity waves become too much worse. They would continue geoengineering even in the face of threat of nuclear retaliation because the consequences would be so dire.