Hi,  I am trying to add a custom racial trait to a homebrew race.  This trait will have 3 different effects, however it will only gain each effect at specific levels.  

The effects are:

• Give advantage to the 'to hit' roll for an elemental spell. 
• Add 2D6 fire damage to the spell. (Only effective for 1 round.)
• The spell caster adds 1D4 to the saving throw DC.

The way I currently have it setup is:  After creating the race, I added 4 Racial Trait Options (Like the dragon born options for dragon heritage), under the Racial Traits Options, I added an action for the above abilities.  After creating the action, I added the Limited Use for it.  After setting the desired limited use, I went to add the Level Overrides to set each effect for the desired level, however the level override only allows you to change specific values, not to edit the effects that may be added at later levels.  

So, is there a way to accomplish this without creating a new action for each ability, with a new set of limited use values for each effect?  Or would it be easier to give all of the effects at the same level, and just increase the number of uses via the Level Override? 

Also, as a side note, I would like to add other race abilities that have class prerequisites.  Is this possible?  For example, a fighter may get one set of racial abilities, while a ranger may get another set, etc for other classes.

You would have to create them as different racial features that each become available at different levels instead of as options.

No, there is no way to put class prerequisites for racial features.