I really think you have been badly advised on this (in the past, not on this forum).
Your building has clearly been run on the basis of a nod and wink and now they are exploiting your sense of right and wrong to bring their by-laws up to date. All the law requires you to do is to give the EC 14 days notice that you plan to change something in your lot. This is not requesting permission – it is telling them what you plan to do.
In the absence of specific by-laws relating to ceilings etc, that's all you need.
Your concerns for what happens if everything goes pear-shaped should be covered by getting a reputable installer to do the work and provide a warranty for it.
The difference between extractor fans and your ceiling fans is that the extractor fans should be repaired or replaced at their (the OCs) cost as they are clearly installed as part of common property.
As for the other unofficially installed fans in other units, if they were there when the current owners of the lot bought them, then they will have effectively become common property even though there was no by-law allowing their installation. So those owners wouldn't have to pay if the fell out of the ceiling (although the original owners – if they still own the units – would).
In other words, if you hadn't removed your fan, it would be common property.
This is one of these situations where I would be tempted to just go ahead and cover my backside by using competent installers (which is all a by-law could compel you to do anyway). A by-law isn't going to protect you if common property gets damaged – it protects the OC against shoddy work now and in the future.
There is a clear inequity in them forcing you to carry the burden of updating their by-laws. It's time to put a stop to it. Send them a letter telling them that you plan to install a fan and that you accept responsibility for any damage it causes to common property. If they want a by-law, they can formulate it and pay for it.
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