There are a few ways to do that.
Do not disrupt or change the plumbing only if nothing is broken or damaged.
Do not resize the bathroom during bathroom renovations. Also, do not change the layout. Use tiles and other inclusions to change the way your bathroom looks now.
Replace the previously installed bathroom accessories when it is necessary. Otherwise, focus on refinishing the old ones.
Choose to go with prefabricated shower and bathtub setup available in Woollahra market instead of having customised setup.
Do not mess up with the electrical system of your bathroom as any disruption will cost you a few extra dollars.