I know people have done it but I would strongly advise against it. The H50 is built to a budget to compete with aircoolers which it does very well. The pump is incorporated into the cooling block and as such is a compromise design. It is not designed to drive multiple loops, longer tube runs or larger rads.
As an inexpensive, reliable, fit-and-forget system it is excellent. I haven't the faintest idea why anyone would mess with that when there are so many cool custom watercooling solutions available that ARE designed for all of that.
I'm looking forward to my next build where I will put together a custom system of hand picked components. There won't be any butchered H50 parts in there that's for sure, it'll all be shiny new anodized specialist parts.