Hi Ralph,
If you add the .asm files into the project the build tools expect these files are part of project and since .asm extension is mapped to HC08 assembler these files are compiled.
There are the options to avoid compilation of these source files:
1) You can rename the files you add to e.g *.txt and add them into the project. ".txt" extension is not used by any compiler. You can check the extension mappings (Project Settings - ALT+F7 -> "File Mappings")
or
2) Create a new target (in case your project has just one) and assign all the .asm files you don't want to compile exclusively to this new target. Than change the target back to the original. The original target includes all the files that you intend to compile (files can be enabled/disabled by the clicking on black dot in project manager -> target icon column).
Stanish