Custom Themes with Play Store Early Access

[sam150122]

I'm running the early access play store version that at the moment seems to be the only version that works with android auto for me.
GitHub version doesnt show up for me no matter how I install it.
Is there a way to add a custom theme or edit and existing theme with the play store version of the app?
I've seen the pr that explains making custom themes but not sure if that's still relevant or if the code for the play store version is is available.
Thank you.