How To Adjust Sharepoint OOTB Webparts Relative Paths

While working on some content query webparts (CQWP), I had the need to apply my own XSLT for styling. So, after building my custom XSLT, I thought I have finished the hard part and that everything is almost ready. Unfortunately this wasn't true. In my ".webpart" file I needed to set the path for my custom XSLT and it popped into my head that I can use the "~sitecollection" token to be replaced by the real site collection URL. So, I did it and started testing my webpart. Unfortunately, it didn't work :( The webpart showed me an error and after...