viewport render has its settings in 3d view properties (N panel) where you also enable it, then switch viewport to Rendered. it might work, because it exports scene a call maxwell to render in background in the same way you do it manually, the difference is it only renders viewport resolution and then draw result on screen
swapping to pymaxwell4 module would be easy, but i am sure it won’t be compatible. pymaxwell api changed a bit also between minor versions and this is major version change…