Modification on Blender with source code

If I bright new tool for mesh, it needs for change and update in blendkernel, blendlib, editor and makesrna, right ?

It depends, usually new tools are added in the editors/ directory but they might require changes elsewhere too. Best is to look at an existing tool that is similar to what you want to add, and see where the code for it is.

A post was split to a new topic: Expected size of setup / package of upcoming blender 2.8?