Is there a way where I can set the sky condition to be overcast for annual daylight simulation? I understand that annual daylight take in the weather data and use the sky condition corresponding to that time/hour of the year. However, is there a way I can set the sky condition to overcast at all time?
If you set the value of direct normal radiation for every hour to zero in the EPW file, all the sky conditions will be overcast, albeit with differing levels of sky luminance (which I guess is what you are looking for).
As to how the values can be set to 0, see this thread: Modify EPW file content