reverse flow radiator

I'm not clear what you want to do. A rad can have its water flow in any direction, the 2 issues to bear in mind are:

1. They tend to accumulate air, this must be let out at the top either by the built-in bleed valve or go up a pipe with exiting water. The former is manual, the latter automatic.
2. Hot water tends to stratify at the top of the rad, cooler at the bottom so you get more heat output if water goes in & out at the bottom. But it still works the other way.

NT

It can be done but only by running to flow pipe down the INSIDE of the radiator to a point close to the lower edge to ensure correct circulation

Have the pipes come down the wall behind the radiator at worst you will see the pipes above the radiator and where they enter the valves at the bottom. Better still use plastic minibore piping sunk into the plaster behind the radiator splaying it out from a wall adaptor plate near the base of the radiator into the two valves. My daughter has this arrangement for all her radiators and you barely see the pipes at the valves. One benefit of this arrangement is that the air release point is where it should be at the top of the radiator.

Richard