Why would the body corporate pay for the replacement of the membrane when it wouldn’t need replacing if the tiles weren’t being changed?
So perhaps your by-law could read:
When an owner chooses to retile their balcony or courtyard, including replacement of the waterproof membrane, the Body Corporate will only pay the portion of cost applicable to the replacement of the waterproof membrane if the membrane is already damaged by normal wear and tear or some other prior unrelated event for which the Body Corporate would normally be liable.
I suggest you contact the Unit Owners Association of Queensland to see if they have any off-the-peg by-laws.