anytime you open a hyd line you have to "bleed" the air out of that line.
So, your answer is YES, if you d/c a brake line you must bleed the system before returning it to service otherwise you will not have any brakes. Air compresses..fluid does not.
Go buy some self bleeding lock screws and some clear tubing. One man can do it quickly and easily. But you DO have to do the whole system. This is where the FSM would be very helpful and worth its $100 price tag. ABS has a specific process to bleed air...
For replacing the master cylinder, you'll first need to bench bleed the new master cylinder before installing it on the car. Not a difficult procedure, but important. Google search it, I'm sure you'll find a YouTube video that explains how to do it (it doesn't need to be Corvette specific, it's basically the same procedure for all cars). Then, once you've installed the MC, you'll need to bleed the entire brake system, starting from the wheel furthest from the master cylinder (passenger side, rear), then making your way to the closest wheel (driver' side, front).
I'd suggest getting a set of Speed Bleeders as well. A think an entire set for the C4 is less than $100 shipped... maybe much less (it's been a while since I bought a set for my '89 so I don't remember the price exactly). Spend the few bucks and go for the stainless steel versions too. They will allow you to easily bleed the brakes by yourself, without the help of an assistant. Just be very careful when you remove the old bleeders to install the new Speed Bleeders. When I replaced mine, I broke one of the OEM bleeders inside the calliper ad (front passenger side) which made it a real PITA to get out! It's understandable when you consider the callipers and bleeders are dissimilar metals combined with the amount of heat cycling brakes experience during regular use. Plus I didn't know when the last time the brakes were bled on my car at the time, so it could have also been a simple issue of neglect too.
And I couldn't agree with boomdriver more: get the official GM Field Service Manual for your car! At $100 it isn't cheap, but it's worth it's weight in gold! Without it, you're just begging for other problems to occur as a result of trying to fix something. If the price is a bit steep, look for a used copy. People are always selling those things.