You can use the Particle Settings to define your own variables that are automatically linked to the particles and can be filled with your own values. These variables and their values can then be evaluated and rewritten using various Emitters, Conditions and Modifiers.
All custom properties for the particles are listed on this settings page, allowing the desired start values to be transferred directly to these custom properties for the new particles created on the emitter.

If there are no custom particle properties in the simulation scene, this dialog page is not displayed.