[zabatron]

Where I worked we used the selector interlock bolt to drain out fluid from IB5/IB5+ gearboxes as they have no drain plug, and it was easy to get to without having to lift car on ramps or hoist,or remove a drive shaft as workshop manual stated.But always use the drain plug if there is one fitted.
Putting gear lever in neutral only applies if removing/inserting the selector interlock bolt as it has a detent ball and spring fitted on inside of the bolt,and you dont want to unscrew it while the detent ball is engaged in any of the gear positions as you risk the detent ball coming loose from spring and falling into gearbox.