Maple displays a defined procedure (yours or Maple's)as output when you enter definition or when you execute eval(). It should be noticed that in either case, Maple uses its own well defined indention scheme, regardless of what indention scheme you used or didn't use when you input the procedure.
Now if you want to edit the procedure, and your only copy is gotten by copying Maple's output to an input line, you will have to deal with Maple's hidden indention characters at the beginning of each line. I have been unable to find any Help material on this, and, in particular, I have not been able to find any way to edit (delete or input) these characters directly. However, they are all invisibly located in the blank space, which is visible, at the start of each indented line. The code seems to be of the form "indent a fixed number of spaces more than the previous line". These fixed numbers are one of three values, a positive number (approx. 3), 0, or a negative number (approx. -3).
Now if you attempt to insert a new line in the usual way (Shift-Enter), it will always be a line without indention starting at the left margin. Then all the following code will be shifted left, messing up Maple's very nice indention scheme and making a visual mess.
What to do? Well, first copy a line with the appropriate indention code from elsewhere in the procedure. Then you can erase all of the line EXCEPT THE BLANK SPACE WITH THE INDENTION CODE AT THE BEGINNING. Finally you can replace the erased code with whatever you wanted.
Changing Maple's procedures is often important, due to errors or omissions in their code or in order to extend it or adapt it to your needs.