Well, I’m not sure what you mean by "routine procedure". In any event, the gearcase extension must be removed with the gearcase as an assembly no matter why you are removing the gearcase. And the same thing goes for the shift leads/harness. So, I guess my answer is that these things must be done everytime you remove the lower unit on this series of engines.
Here is the parts breakdown for this gearcase:
http://www.marineengine.com/parts/johns … case+Group
You will see that there are six studs that run through the gearcase extension and gearcase, you will see the locknuts sticking through the bottom of the gearcase. There are also two bolts toward the rear/top of the gearcase extension that must be removed. I should have started this paragraph with removing the shift harness lead connections that come out of the exhaust housing near the top of the motor pan just under the powerhead, these must be disconnected first before attempting to remove the gearcase/extension housing. These shift leads are a little tricky to disconnect because of the Chinese finger rubber boots over the actual knife connectors. Don’t ever cut the leads to avoid messing with the knife connections, these harnesses are expensive/hard to find and install.
Now, back to my question about whether this engine had been used in fresh or salt water. Removing this gearcase could be quite a fight if the engine has been used in salt water, corrosion tends to build up around those studs making it difficult to slide the gearcase and extension down over the studs. Why is it that you are removing the gearcase?
I would politely ask your technician if he has ever worked on an OMC electric shift gearcase, then ask if he has ever tackled one of these 100hp units, this gearcase set up is unique to this model. A young technician is not likely to have ever worked on something like your engine before, and you probably don’t want him experimenting/learning on your engine.

Nothing to adjust really, just have to make sure all the electrics are working correctly and the alternator is working properly. The engine won’t shift properly if battery voltage is low, and worse yet, it may jump out of gear and be damaged. Your shift switch could be intermittent also, the only way to confirm wiring/switch problems is to check for 12 volts on the forward lead at the knife connection while the engine is misbehaving.
Did the mechanic change the gear lube? If so, he probably used the wrong lube. Only the OMC "premium blend" lube can be used in this gearcase, regular gear lube might cause the engine to not shift or slip out of gear.
The electric shift gearcase is fairly robust, but there are a few NO NOs that can cause problems and damage. I’m thinking you should not use the engine anymore until a more experienced technician can look at it. Where are you located, perhaps a club member in your area could help you out or make a recommendation for a tech who is experienced with the electric shift gearcases.