If I could, I'd use knitr for everything but there's no getting around the utility of comments and tracked changes for collaborative science. This is particularly true when writing grants. For this purpose, I have created an RMarkdown-to-Word template and a cls for references. It's not perfect but it's a start (I couldn't find any other resources out there). Have at it and let me know where you see room for improvement. And, in case it doesn't go without saying, I make no warranties about these helper files being consistent with guidelines. Good luck!
p.s.: If you're new to using RMarkdown-to-Word, you'll probably find this page very useful.