I prefer Resource Hacker for .dll modifications, Photoshop for image editing (in case you want to modify extrated images from .dll files), and some Icon resizer software so you can easily resize icons which .dll files need, like imageres.dll, do not use Resource Editor and try to use drag & drop feature, file will become corrupted and therefore it will not work though you replace it and then your computer will not boot anymore, my suggestions is very simple, pay attention while modifying any .dll file if you want to boot your computer after that, it's always hazardous to modify .dll files.
And one last and most important thing, do not try to open and modify any .dll file in its original location, always copy/paste the .dll file you want to modify somewhere else, then open and modify it.
My suggestion:
1. Original.dll
2. Modified.dll
3. Backup.dll
4. System Restore point
PS: Original and Backup are the same thing but still for caution, you never know what you will mess up.