How to modify the auto generated Makefile in ARM DS?

I am trying to figure out how to modify the contents of the auto generated Makefile in ARM DS. Currently it deletes all .o, .d, and .axf files.

My linker creates some .txt files and a binary and I have a post-build command that produces an image file. I want to force the make clean to also include the linker outputs and the application image. Is the auto-generated makefile modifiable so that I can add those files to the clean function or do I need to write a script that does this?