Rename Variant Label

Use this code to the Custom CSS box

/* rename Select Color variant label */
.variant-option:has([data-text="Select Color"]) .variant-option-title {
    visibility: hidden;
}
.variant-option:has([data-text="Select Color"]) .variant-option-title:before {
    visibility: visible;
    content: "New Color Label"
}
/* rename Select Size variant label */
.variant-option:has([data-text="Select Size"]) .variant-option-title {
    visibility: hidden;
}
.variant-option:has([data-text="Select Size"]) .variant-option-title:before {
    visibility: visible;
    content: "New Size Label"
}

Result: