How to do partial retopology in blender?

Question

3D

I have a model of the monument. Very heavy. You can replace fairly large areas with large polygons (flat areas of the stand, tower) and thus significantly lighten the file. It seems that everything is clear, we do retopology as in the lessons and it's in the bag. Only here it is not necessary to do a retopology of the entire object. There are a lot of different figures. Their condition satisfies me.

Question: how to connect new large polygons with the rest, which you don’t want to reposition at all? Who knows what-nibul trick in the blender?

https://yadi.sk/d/pdW4ld-ScKpkzA

Answer 1

Here's what happened. It was a hell of a job.
https://yadi.sk/d/fFY_0_MYH56o0Q
Dance Macabre
Thanks for the advice. Judging by the description of the modifier, you are right. The chalk was carried in the wrong place. I hope that this modifier can work with selected areas, and not just with the whole object.
And there was also a problem with artifacts - sharp pits directed inside the object. By modeling they are extremely difficult to remove, as far as sculpting is concerned, there is nothing good there either. Maybe there is a suitable modifier for this case?