Hello,
The documentation is there, and the guidelines are also present. The SWAT I/O manual describes it all in great detail.
Technically, it it the lack of understanding how the model works.
Your model is a combination of TEXT files, usually in the TxtInOut directory.
ArcSWAT, SWAT-CUP, anything else that has a name of swat+something is only a GUI or tools that you use to setup your TEXT files (model).
Hence the question: "when changing the values of the parameters (for example CN, USLE-P...etc for terracing). do you have to rewrite swat input" is immediately answered, when you consider what is the swat model input.
All the best,
Natalja