There are kits available that prime the oiling system before starting. I thought about this at one time and was very close to building one for my 240D.
Then a wise friend pointed out that engines almost always go down with UPPER END problems, not lower end. This does not alleviate the need for oil changes, because cylinders and valve train components require clean oil too, but they typically get it anyway.
I'm not saying the prime system would be a waste, it certainly couldn't hurt. But it would probably not extend the engine life before you have to tear it down. The engines I've torn down in my life that were high mileage and worn out, typically had bad cylinders, rings, and/or valves. The bearings usually looked pretty good.
If you really are going to just keep rebuilding an engine and keep it going, the priming would probably save crankshafts from having to be reground. However, in a diesel, you don't have to do this anyway, unless there was a catastrophic lower end failure of some kind, which the priming would probably not prevent. The diesel crankshafts go through a hardening process and only rarely have to be turned at rebuild time.
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in