I finally updated my mod for Airport CEO. Uses UMF (Unity Mod Framework), which has to be installed first (super easy).

The mod:
https://umodframework.com/mod?id=13

Mod Options:

• BaseSalary : Edits the salary all employees want, Executives are 4x this, Janitors are half this. Set to 0 to disable. (Valid range 1-200)
  
• TougherConcrete : Makes concrete runways and stands MUCH more durable.
  
• OverrideSkills : Makes all new potential employees have nearly maxed skill. Couldn't max it as they don't show up in the list. Odd.
  
• CleanerPeople : Makes general floor tiles far more durable requiring less cleaning by janitors. Helpful in large airports.
  
• MasterDebator : All contract negotiations are accepted, regardless of how unbalanced the terms are.

Now if you enable either BaseSalary and/or OverrideSkills the mod ensures employees stay happy. Otherwise you'd have your entire workforce quit.

You can enable/disable any of the options to pick how you want to play. You could even make employees MORE expensive by increasing their base salary, like set it between 16 to 30 for more challenge.