Well, I don't know how much more/less is involved in resealing a 2.5 diesel vs a V8, but the seals you are referring to will require significant disassembly to R&R. Difficulty is all relative, to me it's just common sense and turning wrenches, but I've taken everything I've ever owned apart it seems like, some people are more intimidated by things like removing the transfer case and transmission.
If it is just the rear main and oil pan, you can get to those without much engine disassembly, but you'll have to remove the trans and transfer case, both of which you'll need out in order to replace the seals in them anyway.
If it were me and it were a V8, I would take this opportunity to tear it completely down and replace all the gaskets and machine the heads etc.
"I have taken more good from alcohol than alcohol has taken from me." - Winston Churchill