I get what you are trying to convey but personally being somewhat of a tinkerer it wouldn't fit exactly
verb [ I usually + adv/prep ] UK /ˈtɪŋ.kər/ US /ˈtɪŋ.kɚ/
to make small changes to something, especially in an attempt to repair or improve it:
He spends every weekend tinkering (around) with his car.
I wish the government would stop tinkering with the health service.
So sometimes tinkering will result in an improvement, gain of knowledge or something else even an innovation, but this part got me thinking that tinkering is presented as a negative thing.
Das ist keine Software, das ist ein Bastel(ei).
Ce n'est pas du logiciel, c'est un bricolage.
(That's not software, that's a ____ )
What your are trying to convey here is that, that software is poor design and quality. Even more is like someone es getting offended just by looking at the code(been there), in which case I'd use the word
noun [ S ] UK /ˈmɪʃ.mæʃ/ US /ˈmɪʃ.mæʃ/ informal
a confused mixture:
The new housing development is a mishmash of different architectural styles.
Farrago - us formal disapproving
Hodgepodge - us
Hotchpotch - mainly uk
Meanwhile I believe that Farrago will fit very well as it is a formal disapproval.
Word forms: plural farragoes , plural farragos; countable noun
If you describe something as a farrago, you are critical of it because you think it is a confused mixture of different types of things.
EG: His own books and memoirs are a farrago of half-truth and outright invention. [+ of]