If you save to CXR, you can in fact resume rendering in the VFB (that's the only way to load in to the VFB at all, in fact - the CIE is what would be used if you just want to do tone mapping tweaks etc.). Also, you can load EXRs into the CIE too, they don't have to be CXRs - but you won't have LightMix and Denoising options in the CIE if you use EXR rather than CXR. Regular tone mapping stuff, bloom & glare, sharpen blur, etc. should all work just fine though.
