Scribus is something I never got into. I'm not sure if you could open one of these files with it, but it's worth a shot since this template is free. 

You could recreate this tool in Scribus by making rows and columns of the same passage. Make each row a different size and every column a different leading. Then, if Scribus has a find and replace feature for fonts, you could theoretically replace said font without changing any of the other settings in the grid. Then, you would, in theory, have an entire document of the same font in all the myriad of size and leading combinations that you created.

If Scribus doesn't have a document-wide find/replace feature, it probably has something like a properties panel where you can replace type there. If all else fails, you can make the passages on the page a paragraph style and then edit the style—but that does require some additional work upfront.

Hope this helps.