Hello,
lately, I've been brainstorming various backstories for my character and came to conclusion that Fighter/Mage would be the most optimal one for me (both from gameplay and lore wise).
But here's the problem, this time I want to roll a human (before I always played elves or half elves) and they can only dual-class. I am somewhat familiar with Shadowkeeper and its uses but I am not quite sure about this particular issue.
After starting the game, should I just change the class from Fighter to Fighter/Mage and be done with it? Or are there more variables I need to change, like THAC0, saving throws, starting spells etc. etc.?
Or should I create a Half-Elf character and then change him into a Human?
Any answer or solution is appreciated! 
BTW: I also plan starting on heavily modded BG2Tutu (No Enhanced Editions whatsoever).