Nope. Not buying it. The common property has not been altered as the planters can be lifted and taken away and everything would be back to normal without the need for remediation.
If I take the wheels off a car and leave it on bricks on common property, have I altered it? I don’t think so. How about if I build a shed that sits on common property but isn’t fixed to it? Same story, I reckon.
Sometimes we are looking to apply aspects of strata law in ways that were never intended. There are times when we just have to apply common sense. There are other strata laws that apply to the car and shed scenario but S108 isn’t one of them.