Wouldn't it be easier to use JavaScript?
PixQL: SELECT WHERE COLOR = #FF0000FF; OPERATE SET COLOR = #00FF00FF
JS : if (rgba=='FF0000FF') rgba='00ff00ff'
PixQL: OPERATE SET G = R
JS : g=r
PixQL: SELECT WHERE ROW % 100 = 0 OR COL % 100 = 0; OPERATE SET COLOR = WHITE
JS : if (!(row%100) || !(col%100)) rgba="ffffffff"