Can't say that's ever happened to me. Usually, I've got characters and such picked out before the doll ever gets here. However, sometimes it's the dolls themselves who influence their own personalities.
For example, I'd gotten a Fairyland F60 Juri sculpt to stick on the muscular body. I'd been thinking the whole time his name would be Artemis and he'd be a warrior/hunter. Well, his head gets here, and I pop in a pair of blind eyes (just because they were the only ones that fit at the time), and instantly realized those were his eyes. I thought, okay, a BLIND hunter. Who never misses his mark even though he can't see a thing! That's cool.
Nope. The more I looked at him the more I realized he just wasn't an Artemis, and he definitely wasn't a hunter. Finally, I put a few spare wigs on him, one of which he also immediately claimed (exactly matched the shade of his eyebrows), and a spare fantasy outfit and realize he's not a hunter, he's a musician. His name is Muse and he has the ability to "see" threads of music and song, and weave them into amazing clothes said to bless the wearer with extraordinary talent, luck, and wealth (so of course I immediately had to buy him a doll-scale lute from the net). Thus, he's highly sought after by human and fae alike. Oh, and he's also the long-missing father of my little elf twins, who have been under the guardianship of another of my dolls since Muse's enemies would use them to force him to do their bidding. Have to say, never saw THAT one coming.
So, yeah. From hardened warrior to gentle (and well-toned) musical seamstress father. Sometimes doesn't matter what, if anything, you've got planned for the dolls. Who needs humans telling me what they should be when the dolls can influence their personalities all by themselves just fine.