I don’t use button-text, but maybe you can get some idea by looking at how to change the color of the button-icon:
card_mod:
style:
mmp-shortcuts$:
ha-icon$:
ha-svg-icon$: |
:host {
fill: red !important;
}
The example illustrates how to move down the DOM tree into the shadow-root elements. I don’t see that in your examples and maybe this is the same challenge.