I found here some answers to my question but I'm not sure at 100%.
I jnow we have to set the project color profile when creating inside AE and/or when merging footage with different color spaces. But if I just import, say a Quicktime 1080p Uncompressed 10-bits that has the Rec.709 embeded, and I just want to re-export it, say to a TIFF image sequence, should I set Color Management to On with Rec.709 or should I leave it Off? Will AE convert the embeded profile to my monitor color profile if it's off? Obviously, I need to set the project to at least 16bpc to keep the original color range, but I'm stuck on the color management of imported footage with embeded color profile.
here's the funky thing, if the output profile color working space is the same as the interpreted footage, then no color management settings actually change anything. It's the same thing as if management is turned on and you go to view-simulate output the same profile, they look exactly the same, nothing to do!
In simple terms, if they're the same, color management turned on doesn't do anything, but the downside is that you can't color correct based off a calibrated monitor, but like you said, you just needed to re-export, so that doesn't matter either. and you're right about leaving it at 16bpc. Don't lose that trillions!!!
btw, a just-4-fun tip is that simulated outputs can actually be burned in creating free-fast-great looking film looks. The effect is called color profile converter. For instance, if you want high saturation, start with a wide gamut or pro photo then strink it down
to a smaller gamut such as SD. There's fuji stock too etc.
I forgot to add, if turned off, you won't have an imbedded profile anymore. So, depending on your workflow, if your other software needs it imbedded or not because AE can assign profiles, some others can't.
I leave it up to you, you can always play it safe and burn in the same imbedded profile.