Yes, many features can be toggled with flags however there is no full control. There is great performance improvement with forced full depth prepass only for scene capture in SCS_SceneDepth mode. Base pass is the bottleneck.
I just did quick test:
Very simple scene, All rendering flags disabled (except static meshes), SCS_SceneDepth, 4096x4096 (launcher 4.18)
vs
Very simple scene, All rendering flags disabled (except static meshes), SCS_SceneDepth, 4096x4096, Depth prepass only (custom build, 4.18)