Whihc model of Shimano brakes?
The earlier ones had reservoir that has to be uppermost. If you fit them upside down ,then that is asking fro trouble as air can enter into the sytem and brakes will get spongy.
All you need to do is get an 8mm spanner, undo the brake hose hollow ut at the brake lever, sawp over and tigthen. You should use a new olive but you probably get away with it.
no need for new hoses (not sure why you said cables as they are hydraulic, right?