The crank arm must be tightened so don't use it to move the chainline. Moving the BB cartridge side to side is ok and standard practice. A little bit of movement can be had just by screwing one side in as the other side is screwed out. If an unacceptable gap develops spacer washers 2 and 3.5mm wide are available. 3.5mm is about as much as you can safely move the BB side to side though and there is no guarantee that this much is available on your bike. Limits are imposed by the length of the BB shell versus length of the BB bearing housing. Some L side cranks start getting really close to the BB shell. If this is not enough, then you may have to go to a longer axle. Steve