Sky replacement for two time lapse clips, 3 seconds long in total

I have two very short time lapses of construction work that I would to have the sky replaced in. I'd like it to be quite subtle and realistic-looking, no clouds sourced from elswhere or anything, just a different colour tone on top of what's there. The first needs to have blue sky and be sunny, the second needs to have a grey sky, just enough of a hint of grey to look different. I have attached before and after shots with mock-ups of how I would like it to look. Also attached is the time lapses themselves! I'm on a very tight budget and it's a very short sequence, so looking at about $10.