MacOS application for XML conversion

I am an editor who works with Final Cut Pro X and I am running into issues with the exported XML files, called fcpxml files. These files comply completely with standard XML 1.0 structure. For my own uses I need an application that will take these XML files and alter some of the data according to a very specific logic. The application will have to change the data and write it back to a file. I want to be able use this in my day to day work and also publish the resulting work on the App Store. I hope it will help editors like me and maybe pay for the expenses of making the app. Therefore it will need to be quite user friendly and complete. For example: check if the imported file is indeed an XML file and report so if it is not. Or if the procedure fails to produce an XML file it will need to report this in a user friendly way, etc. The application should be developed using Swift 4 on the latest Xcode 9 I have a good understanding of what the input XML files are like and what needs to happen. I have some basic knowledge of Java and Swift to be able to interpret roughly what goes on in an application. The code will need solid commenting and naming of functions etc so I follow roughly what happens where. I hope someone is willing to take up this small but interesting project.