"I have heard of no eu court ruling modifying not legal."
Of course there are laws in the EU covering modification. I'll just point at https://en.wikipedia.org/wiki/Computer_Programs_Directive where it mentions "the translation, adaptation or other alteration to the program" as being the exclusive right of the copyright holder. Then there's Directive 2004/48/EC of the European Parliament and of the Council of 29 April 2004 on the enforcement of "intellectual property rights".
I'll also point back to the GPL again and how it relies on laws like this in order to be able to function. So look, for example, at the GPL enforcements actions that Harald Welte brought in the EU. If modification were not the exclusive right of the copyright holder then this aspect of the GPL could not be enforced and Harald Welte would not have been as successful as he was.
