Moral Dilemma

As being relatively new to paper modeling I am usually busy with at least 2 projects at any time. One, a project that challenges my skills, and Two, a quick fix project that I can complete in a few days. Currently my No. 1 project is Andrew Ingwalds Spitfire that I downloaded from here. I love how everything fits together absolutly perfectly, and the only limitation is my own lack of skills, and a bad print job. Plan to reprint and rebuild once I have finished the 'pre build'. Project No.2 is a Modelik Yak 3 (1:33) that my daughter brought back from Poland for me recently. I have made scans and working of those due to the fact that I still make a lot of mistakes that I have to redo. I find lots of small mistakes with the model, like a few lines that do not match up, and I am not a big fan of building bulkheads in sections as I tend to get the alignment off ever so slightly and it spoils the model for me.

My dilemma is would it be morally ok for me to trace my scans of the commercial model and modify it so that I get the result I am looking for, or should I obtain permission from the designer before I do it?