There could be times when you need to replace a system file in windows 7, but in order to you would need to take ownership of that file, for this we have recently written about how to quickly take ownership with right click context menu. But if you want to avoid this situation of taking ownership you can use this free utility called Se7en File Replacer.
We had covered some other similar other ways to delete or replace a system file. Here is how you can replace a system file with this tool
In order to replace the system file with the modified system file, drag and drop the modified file over this replacer utility. It will automatically look in "system32" folder, and if the old file is found it will be backed up and replaced without prompt, otherwise you can select it manually.
It also allows you to replace a system file which is in use, as it will end the process using the file and then after running it will automatically start the process after replacing is done.