The syntax you mean is
but this will render the value label for 99999998 an empty string, which still is slightly different from no value label at all. To completely remove the label, you must use "value labels" and respecify all labels for each variable except for 99999998. I think the only serious option for doing so is writing a little Python script.
Mind you that "value labels" starts with removing all value labels
for the given variable(s)!