How to add old master integration files to new lights to be integrated

You can make 2 separate integrations, then reload those in as new lights and do the integration of those again.

To develop a bit more on this: there are 2 main things you want to achieve when deciding how to combine multiple sessions:

- Get the best out of the data in terms of noise and quality
- Ensure outliers (satellites, etc, but also star bloats from bad seeing/focus) are well taken care of

The first point I honestly would not say you have a huge difference in terms of quality when stacking multiple sessions vs single big session, and the gain in time is very significant, especially until we can save sessions to stop-and-continue (ahem, very subtle hint? 😍).

The only real risk is the second: when combining pre-stacked chunks of your images, if you have outliers that have remained on your individual sessions' stacks, you risk not having enough images in the final stacking to get rid of them (e.g. imagine having 2 sessions only each with a leftover streak from a satellite in different places). Whereas if you stack everything together you're much more likely to get rid of outliers completely.

If you have 20-30 images or more on each of your sessions you can probably just add the stacks together, but if you're working with very few long exposures that can be an issue.

Hope this helps!

p.s. if you're stacking the big pre-stacked images you might as well do light pollution removal on each of your session stacks to get rid of big gradients prior to stacking them