I made the change to the table configuration for realtime table. But it does not take effect. Do I need reload all the segments?

what change did you make?

I added transformConfigs into ingestionConfig

it will apply to the next new consuming segment AFAIK. I think it should probably work if you reload segments, as long as the messages at those offsets are still in the streaming provider.

I tried to reload the segments. It did not work. By the way, is it possible to flush the consuming segment manually?

I don't think you can. But I'm sure someone else asked about that recently. @Mayank would know

Transform config treated as backward incompatible change, and hence not allowed.

not allowed as in it's ignored for already consumed segments?

Transform config change is treated as backward incompatible change. It is not allowed for existing consuming segments. Is it allowed for future consuming segments?

Flush segment on-demand feature is in the design process now.