You seem to be very well-informed so I'll try my luck here.

If I need to only change a wall design, but without any extension, is there any kind of plans drawing or approvals needed?

The renovation will definitely change what it looks like from the SNP architect drawing, but no extensions whatsoever, just change the "design" of the wall, patching up some big grills into windows.

Then is there any CCC or approvals needed? How much generally drawing cost if it's only one face of the house (the back)?

Hi bro, did mpsj officers come check your house before architect issued ccc?