Normally better program comprehension means easier program modification. I think DSLs break this: They increase program comprehension, but I bet they make (some) program modifications much more difficult due to the lack of tool support in the most DSLs.
I agree the lack of tool support for most Domain-Specific Languages (DSLs) makes difficult to handle in one way or another.
Just yesterday I wanted to search for the definition of a function and failed at the first try. It happens that the function was generated with a macro in Emacs Lisp. Had it been defined as a normal function, it would be much easier for me to locate it in the source file.