If you treat the Learning Phase of xNN design as "Compile".
It remind me of the my first FORTRAN Program.
It was code on "Punch Card"
Each card represent one line,
If you write a hundreds lines of code.
You will get a thick program.
Then you put it in a basket in front of the computer center, and wait.
The next day,
You will get the cards warp with the result print out.
Maybe it is
"Divide By Zero Error"
"Or a lo of garbage "
the result you expected.
Sound like xNN
The only way to reuse you code is literally "Reuse" ,
You remove the code from one part of the program and move to another program.
Hope you won't mess up the variable and label name.