Sounds a lot easier to change out than the five cylinder. If you can access the bolts in the clear from above it is probably no worse than the average starter. Make sure your allen key bit fits well though as sometimes the top bolt is really tight. Also make sure the allen bolts are cleaned ouit and that you bottom in them. Even if it rounded out though you could probably grind off the head of the bolt. Or saw it off.
I have never changed a 240d starter but have had the enjoyment of the 300d that you have to pretty well access along the top of the transmission for the top bolt. It was harder but once the top bolt broke loose not bad at all.