I’m with KP for the most part. I reckon someone from the EC has had a sticky-beak when the apartment was being shown for sale and has noticed some unauthorised changes to common property that, technically, are the Owners Corp’s responsibility even though the changes went through without their approval or knowledge.
First things first, they can’t make you take them out at your expense so make it clear to them that they need to back off or you will be the one taking them to the CTTT. However, they could force you to allow them to reinstate the ceiling at their expense (but, seriously, that is not going to happen).
A compromise, as KP suggested, would be to accept responsibility for the ongoing repairs and maintenance of all the common property that was altered by the previous owner (which I too suspect is all the EC really wants).
So tell them that if they create a reasonable special resolution by-law that allows you to keep the apartment exactly the way it is, you will sign the agreement – provided they pay the legal costs.
Otherwise they should leave you alone and they shouldn’t expect to hear from you again until such times as you need them to repair the lights, plumbing or whatever else was changed in the renovation.