Newbie question: adding more data to FITS?

Hello APP'ers,

Am currently running the 30 day trial of APP and have had some success with with a widefield of M42 & Horsehead shot at 200mm with Canon 5D mk iv raw files. I'm trialling APP because DSS won't process my 5D mk iv RAW files (works ok with TIFFS) - something to do with DCRaw I think.

Last night I tried running APP against a different subject, with 93 light frames, but after 2 & 1/2 hours number crunching my ageing Windows 10 PC spat out a black rectangle with barely any data on the histogram. Very frustrating! The only difference between my success & failure were more frames for the failure (93 versus about 25 for successful M42) and I didn't add any darks for the failed image. I used the best 80% of the 93 frames & used default settings...

My question is, seeing as my PC is rather slow, can I run APP on say 10 light frames + darks, generate a FITS file from those, and then add in more light frames to add to the FITS file later? I.E. without having to process all 93 frames at once (and wait 2 1/2 hours!!!) ?

Hope that makes sense!

Thank you in advance,

Stephen.

P.S. I will be away from my PC for much of the rest of today so please don't think I am rude if I don't respond right away...