1. Definitely, but the scope taking legal action fall under local council. JMB/MC is not empowered to take legal action on turning residential to commercial activities. But JMB/MC can cooperate with local council to take action on the issue.

Illegal converting into commercial activities will eventually "destroy" the property value in the future. So no benefit to any owner.

2. This is impossible task to carry out, as resident has the right to use the common facilities unless special issue arised, like no paying maintenance fee, always causing nuisance to neighborhood etc.

3. No owner has the right to take any action on the common property issue, apart from JMB/MC appointed. JMB/MC cannot empower all owner to take action, it will cause more chaotic situation. It should be done by security or JMB/MC itself.

JMB/MC cannot/shouldn't simply change house rules without any notice or convene EGM or through a proper meeting and clearly in the minutes meeting

The strata title act is not comprehensive enough to start with.
So there are plenty of grey area.

To specific answer the question.
The act didn't stated JMB/MC has the right/no right to cut utilities supply if maintenance fee is not paid.
Unless there is court precedent ruling said so, then we can refer to.

Utilities supply is between owner/utilities company.
JMB/MC has no right to intervene.

But the issue is we know water supply come,

Utilities company --> apartment/condo tank (a common property governed by JMB/MC) --> owner.

So grey area arised on the common property (tank), piping in the common property side of issue.
JMB/MC has no right to turn off the tap within owner premise, but the tap is at the common property which fall under JMB/MC responsibility. So how?

So no black and white stated the issue so turn into grey.

By right, owner needs to inform management that the unit is rented out to whom.
This can be stated clearly in by law.