Oh, yes, the good ol' yank out the alternator deal....
Remote chance the only thing that was wrong with the old one was the voltage regulator ?
Most of the time V.R. is what wears out due to two friction contacts and very rarely does the alternator itself go bad. When the contacts wear down, charging becomes intermittent until it does not make any contact at all.
The V.R. is mounted on the alternator with two screws and there are no wires involved.
There's a chance you may need an extremly short screwdriver if space is tight.
This is what I'm familiar with among the diesels, and I suspect most others are similar.
Good luck, and hope you have the opportunity to examine the older unit if it's still around.
I'm wondering if the shop should've checked the V.R. first ?