Wants to use User defined Macro in Makefile

I am converting 32-bit C++ code to 64-bit on Solaris.
I have used unsigned long in number of files. I want it to convert to unsigned int for 64-bit.

Total files are around 2000. Can you please help me if possible to do it in makefile using MACRO while build.

If it is not possible any other way to avoid to make changes into 2000 files. Does in one shot we can do it?

Isn't that part of a code change and I think datatype should not be a parameter determined in the makefile ( I might be wrong? )

So any other way to do it or i have to go to respective file and has to make changes?