I'm facing a problem when using https://www.fluttericon.com/ to create my own customized flutter icons. Whenever I put a set of SVG files to this link, it will return me a zip file as described below. 
However, if I have some new customized icons want to add to my current list, I cannot put that new set to https://www.fluttericon.com/ then get the result for the new set and add it to the current one in the code, but I need to generate the whole set(old ones + new ones) again to make it work properly. It is very cumbersome when I have to download the old one and rename every icon again.
Thus, I want to ask for any proper way to avoid that problem or the proper way to use this https://www.fluttericon.com/ and its result in code.