Apply changed to default theme

Maybe you can help me…
I’m fine with the default HA themes, but I’d like to add some variables in order to make it easier to have consistency throughout the dashboards and cards.

For example, I’d like to add this set of values to the standard theme:

My theme addons: 
# heatpump:
  heatpump-online-color: green
  heatpump-offline-color: grey
  heatpump-warning-color: orange
  heatpump-compressor-color: teal
  heatpump-heating-color: var(--purple-color)
  heatpump-hotwater-color: var(--deep-purple-color)
  heatpump-antilegionella-color: var(--pink-color)
  heatpump-cooling-color: indigo
  heatpump-defrost-color: cyan
  heatpump-standby-color: grey
  heatpump-auto-color: green
  heatpump-eco-color: green

Is there a way to add such a limited set of values to an exiting theme, without bothering about the theme-yamls?

Or should I create a complete new theme, taking the complete HA-theme a basis? (I couldn’;t find it)… I checked frontend/src/resources/ha-style.ts at f9844e8e58569d485b66838c11a9eb9632540f5d · home-assistant/frontend · GitHub , which contains many variables, but which is not a yaml.file.

Tip are welcome!
Thank in advance