You'd have to set up you Octane setting differently for both shots, and this can't be done in one take unfortunately. You could set up multiple render targets (one for your high-quality image, and another for the low-quality part), and render those back-to-back.
Hi Xhed, thanks.
Yes, I know I have ...

I have a stereographic 360 scene with small animation, I want to render this in 4096 x 4096px, but it would take a long time to render the whole scene as animation. So I,m planning to render the static part as high quality still image, and then render film region the animating part in medium-low ...