We had a similar situation in our block, tenant went ahead and arranged for a bidet install without looping in the owner or the strata committee. Honestly, these things always end up messy if the right steps aren’t followed from the start.
In our case, we asked for proof that the plumber was licensed and insured before anything got approved. I’ve used Your Choice Plumbers in Melbourne before (not for strata, just at my place) and they were great, proper paperwork, knew what they were doing, especially with backflow prevention.