Xanterith said:
So what you may want to do is set something up like that and keep track in secret of the player's alignment. Let them know when to update their character sheet, and that's it. Have their actions guide their alignment.
I do this IMC. I have my notes for each session, not the adventure info, but like scrap paper that I use for personal notes and running totals, stuff like that.
I make a table with the PCs alignments, so it's there to see easily all the time, and occasionally jot down +1 evil or +1 chaos, and a small phrase as to why. +1 evil, killed old lady or +1 law, helped city watch. I only give merits, not demerits, so it is not relative to their current alignment until I total up over 10 points in one direction.
Usually my players do a good job, and if they get to 5, I give them a warning ("Hey, you are building a history of acting chaotically...). That's how I keep alignments in line with behavior.
If I had a player approach me and ask to change alignments, I'd only ask if it was to pick up a different class to twink out their build. If the answer was no, then no problem, their alignment will follow their behavior. Immediate, oppositional alignment changes are for cheese.