| Yes, just un bolt the motor mounts and jack up the engine. You are being way too paranoid about changing the oil when you are done. I work at a BMW shop and we never have to do anything like what you are talking about when we change an oil pan or pan gasket. Just make sure your new parts are clean and you will be fine, there is no need to waste 15 liters of oil. With your new oil pump so it doesn't cavitate on initial start up pour some oil in it before you install it and spin it arround a few times by hand. This way there will be proper sealing of the gears in the pump so it will pull oil and not air. | 
