I rendered out an .EXR image sequence (300 frames) at 2000 samples. I opened up a brand new blend file and imported the images to add a "glare" effect in compositor. When I re render out these images (with the glare effect) does the render samples affect the output? Better yet, What in the render tab effects the image sequence with any added effects?
Samplings do not count in the Compositing process.
If you don't have any RenderLayer Node in the NodeTree, the 3D scene won't even be rendered, but the nodeTree will so, it doesn't count. You can have strange artifacts in glare if the Quality of the node is set to low.