Modifying G-Buffer MRTs format?

In our current project we've stumbled upon a very specific bottleneck: we are limited by CROP and memory, meaning that writing to the render target is more expensive than running the shader. The game uses deferred rendering and MRTs 0-1 use ARGB32 as their format.

One very suitable optimization for such a situation would be to modify the render targets: reduce pixel count, the amount of MRTs and change their format so they would require less memory and bandwidth. Unfortunately, we've only been able to change the emission/final MRT format (from the graphics settings).

Is there a way to change MRT texture format in a legacy pipeline?