building design plan is important or house registration

Report the same through Regd post  to  Commissioner Municipality/Corporation with such photographs.

The facts as posted lacks clarity. Olease post the simple facts.

The encroachment of the parking space which is existing as parking space since the construction of the apartments is nothing but an arrogant and illegal act.

The building owner has no right to open entrance on his own on whichever side he may desire.

He has to adhere to the building construction approved plan only for all  such things.

His illegal activity may be brought to the notice of the local civic body and if they fail to take any action  on this and if you are affected by such an illegal act, you may file a suit for mandatory injunction against the owner and you can implead the commissioner of the  municipal corporation as necessary party seeking direction against him to demolish the entrance and remove the obstcles in this regard if the house owner is not complying with the court orders in this regard.

The building was handed over 25 years ago (after registration) as "commercial", how the status is found to be "residential" as per approved plan ?

Encroachment is altogather a different issue in a commercial building.

Be clear and specific, your statement is vague.

It is advisable to consult a local prudent lawyer for better appreciation of facts/ documents, professional guidance and necessary proceeeding.