Hi!
Just open the universe.ini in Data/Universe search for your system.
Omicron Alpha is Hi01 and Gama is Hi02. The line visit defines, when the system will show up on the navmap. Here's what options you have:
0 -> system shows up when you first visit it
1 -> system is shown from start (you do not need to visit it)
128 -> system is never shown (even if you visit it. It's like the two unknown systems)
Remember that with these changes you only make the systems visible (the small stars in the universe map). To make all bases, nebulas, etc. visible, you need to go to the ini of the system (for Alpha it would be Data/Universe/Systems/Hi01/Hi01.ini) and change the visit lines for all the bases, nebulas, etc. also to 1. Then you can see the whole system with bases, nebulas, jumpholes, etc. from the beginning.
So the visit line works for every object!
There are also some other visit values for special things like wrecks and some nebulas, but I think this is enough for the basics. If however you need more values just post here.
I hope this helps!
Black Eagle