Hello,
If you create a new target within existing project you have basically two options. Either create the Empty target or clone existing one:

If you select "Empty target" then you need to setup all the project target settings manually.
Therefore I'd suggest you to clone the existing target that is most similar to new config you need and adjust the target settings only.
For .elf file you need to change the file name since cloned project shares the original file name:

Regards,
Stan