Tweaking reports javascript?

Many years ago, it was possible to customise reports by tweaking the underlying javascript in templates.

I just downloaded an evaluation of Toad Data Modeler and it looks like this is not possible anymore...

Is there a way to create a customised version of HTML reports?

it is still possible. See topic "Feature and Tools -> Scripting and Customization-Scripting and Customization Samples-> Modify HTML Reports" in help.
I'm not sure what is accesiable in Trial version.