What happens when you change Web.config?

Question

ASP.NET

There is such a file: Web.config it stores the necessary ones: In the directory with this file there is a folder: /xxx/ in which there are several hundred .ashx handlers The question is whether all ashx files will be recompiled or not? If so, what is the best way to make a variable that was in 2 files and before changing it did not have to recompile everything. The option to duplicate in 2 files disappears
<add key="key_name" value="key_value" />