My sim likes his job but he isn't ambitious and doesn't want to get more responsibilities. He should be able to refuse a promotion.
Of course the consequence is that he will lose this opportunity to be promoted for a while.
After 3 refusals the promotion will be disabled permanently.
It also feels unrealistic to get an unlimited number of jobs at career level 10, the sims should compete with the current sim at level 10 before being promoted. The consequence is that the current sim at level 10 will be demoted, retired if elder or fired if your sim choose to sabotage.
Which means NPC level 9 coworkers can try to challenge your sim at level 10 to get the job.
But be careful because Mean/Evil/Ambitious coworkers won't play fairly.
Career level 10 won't be a dead end, it would become a new challenge.
For the players who don't want it, an option to turn off Career level 10 Competition.