The problem with the data upload limit for attachments has been fixed. I have restored it to 30MegaBytes. A recent forum software upgrade was responsible for the changed limit. Please accept my apologies for missing this when upgrading the forum sofware, Mabula.
Yes, one can! As a test I ran m45 subs from 2 nights, one set at ISO 1600@30 sec and the other set ISO 800 @ 60 seconds. Together they made up to 11,010 seconds, or ~3hr. little post in Lightroom and PS. I used the Batch modify tool to crop the best parts of the mosaic looking Integration so as not to have to do any work on that part.
Yes, as you found out already, it's certainly possible.
One tip, if you combine data of different iso values and exposure times, it can be beneficial to change the normalization mode in 5) to multiply-scale instead of add-scale 😉
Main developer of Astro Pixel Processor and owner of Aries Productions