In my opinion, if the internal doors are added to an existing framed opening then that should present no problems as no structural issues would probably be involved. This would probably be deemed to be a Minor renovation, however in certain circumstances it may be deemed to be a ‘Cosmetic’ work if only things such as screws, paint, and fillers are applied to the walls. You may not need approval from the OC if it is ‘Cosmetic’.
If a wall is being ‘opened up’ to install the doors then check whether the internal wall is a structural load bearing wall. If you are intending to ‘open up’ a wall then a structural engineer should be able to advise you. Try and obtain a copy of the original plan. ‘Opening’ a wall would probably be a major renovation.
Building or installing a small pantry on an internal wall should present no problems. Pantries are often modular. If you are not undertaking a full renovation of the kitchen and the pantry it is merely screwed to an internal wall then it may be deemed to be ‘Cosmetic’ work rather than a Minor renovation. You may not need approval from the OC.