The only difference on the off and on message is the third last byte- $00 and $01
So the button should be programmed ...
.showvalue on
.minmax 0 1
.default 0
.mode toggle
.tx $F0 $42 $30 $00 $01 $19 $41 $61 $00 $10 00 val $00 $F7
When the BC is powered up it has the default in val (0 = min)
Pressing the button flips it to max ie val =1
The output is
$F0 $42 $30 $00 $01 $19 $41 $61 $00 $10 $00 $01 $00 $F7
Pressing the button again flips it back to min ie val =0
The output is
$F0 $42 $30 $00 $01 $19 $41 $61 $00 $10 $00 $00 $00 $F7
All the best
Royce