I have done that at Kodak. As long as the surface iodide is the same, there is no exchange in halide, so it might be a 10% iodide and a 5% iodide, but if both are core shell and they have the same surface, ie pure bromide or 1% iodide, mixing them has no adverse effect. Temperature has no effect whatsoever on the mixture. Crystal habit has no effect on either emulsion.