Yes, it worked, thank you.
I rename the file to max 8 character, (although the software user guide suggest max 15 characters)
As you suggested, I had to open a new Caesar 2 file that the new unit file can be used in it from start. I picked the new unit file, saved the new Caesar 2 file, and later I imported all my existing 3d model into the new Caesar 2 file.
Now I am able to use non nominal pipe sizes example (2.000") and it wont convert it automatically to a nominal pipe size (2.375"). Thanks for helping me.