I changed mine. It's not too hard.
There was more angst in thinking about the work than in actually doing it. :)
Here's the procedure and pictures: How to replace a 540 radiator
I actually did this twice. The first replacement radiator I put in was defective. Looks like it was damaged in shipping. If you do this a couple times you can get quite good at it! :)
Although my car is an automatic, there were no connections to the transmission to worry about. Maybe that is also the case on 94 540i's.
This diagram may be helpful: Radiator Parts Diagram
Since I had to be up under the car anyway, I took the time to flush the cooling system. This is a little more involved; you need to drain coolant from the block, too. There are drain plugs on either side of the block.