In order to sum up the comments, the statements are the following:
- In order to change the file name
In [1]: import pathlib
In [2]: path = pathlib.Path("/home/user/to/some/folder/toto.out")
In [3]: path.parent / "other_file.dat"
Out[3]: PosixPath('/home/user/to/some/folder/other_file.dat')
- In order to change one part in the path
In [4]: parts = list(path.parts)
In [5]: parts[4] = "other"
In [6]: pathlib.Path(*parts)
Out[6]: PosixPath('/home/user/to/other/folder/toto.out')