I have S32K142 software that was written using Notepad++ and built into an .elf file using a makefile. I am able to use IAR Embedded Workbench for ARM 8.40 & pemicro multilink to flash the software.
I imported the existing elf into IAR following these steps: Debugging an externally built executable file | IAR Systems

I am able to "download and debug" the program using IAR and my PEmicro Multilink. The debugger initially stops at main() like I configured in the debugger options menu. I am able to resume and pause the debugger. The correct C file will pop up in the IDE with a line of code highlighted green. So the debugger is able to find the source files that are elsewhere in my PC that I used to build the elf file.
My question is how do I set breakpoints in the C code myself before I start the debugger? I have tried Project > Add Files and added the files I want to debug. However when I try to flash the HW, I get build errors from the newly added C files. I IAR is trying to build the C files added to the project.
Ideally I want to use Notepad++ and makefile to edit and build the source code. I just want to be able to set breakpoints and debug the code using IAR. Is my only option to create a new IAR project and import all the source files, linker, etc?