I'm sure those who use a custom template to start new games already know this, but that's one way to get around having to cancel the story mode for new Sims if you don't want to use it. I use a custom template myself and used that to open the game and create a new Sim to try out the feature tonight. When it opened it was at the old way of making Sims.
If you do still want to make a Sim using story mode in a custom template, you can. Just click to make a new Sim along with the default Sim you get and choose the icon that looks like an open book. It'll open story mode for the additional Sim. You can then just delete the default Sim when you're done. I hope that all makes sense?
EDIT:"GrumpyGlowfish;c-17164485" wrote:
I experimented a bit and found out that if you save a story sim to your library and load them back into CAS later, you can edit their traits and aspirations, but the preset job, skills etc. are gone - or at least you can no longer view them. This means this feature is only useful if you create a sim from scratch and start playing with them right away. Makes it even less useful for me, sadly. (And it makes me wonder how exactly those new cover sims are going to be implemented, I assumed they would come with preset skills and jobs as well.)
It can come up with some funny results, though. The first (and only) sim I created this way got the Good trait, but also the Public Enemy aspiration!
I had some weird results too. I created an elder using story mode and her aspiration was "Big Happy Family." lol Um, elders can't have children. I guess she could always adopt, which might make for an interesting story. *shrugs*