Yes.
Open the console and type "ShowClassMenu" That'll open up the same menu you use at any other point to define your class.
Click "Custom Class". The game will display a summation of your original choice, but when you go through the subsequent menus, it will not have those choices already highlighted, so if you're going to have a hard time remembering exactly what you chose, make notes of it. Then re-enter all of that information, plus whatever changes you want to make.
Keep going through the menus until you get back to the original one. Do NOT click "Done". If you do, it will reset all of your skill advancement. Instead, with the console still open and the menu still on that page, click the esc key to open the save menu and make a new save, then click esc again and load that new save.
And that should do it.
Note that this won't change anything other than your majors and minors (or specialization, or whatever you change). It won't change your skill levels to reflect the changes.
When you first set the character up, any specialization skills gain a +5 and all your majors start at at least 25. When you're talking to Baurus or again at the sewer exit, any changes you make to majors or spec rearranges those +5's and 25's. But changes you make through the console, using the above method, do not. If you click "Done" on the last menu, the game apparently tries to do that, but it doesn't do a very good job of it. It changes values, but they don't seem to end up what they should be. AND it completely wipes any experience you've gained on the way to your next skill increase-- all the skill bars are reset to zero. So using the esc and save method avoids that, but it means that if, for instance, you make a minor that had a skill level of 5 a major, you now have a major with a skill level of 5. If you want to change that to the 25 that it should be, you have to use something like Player.SetActorValue to do that.