About 30 hrs of very hard labor. Trust me. I have done that job.
You cannot replace it without pulling the engine. The seal will is cheap, but it is a rope and the engine has a pin in the cap and in the block that drive into the seal. That means there is no way possible to get the old seal out and a new one in without splitting the engine case and pulling out, or at least lifting the crank away from the block.
There are a lot of details between here and there. Let us know and will sort out some stuff to do to get it right.
Best get set for a big job ahead.