To be fair, the exact sentence is "we like to tone them down about 10%", which suggests a more common practice rather than only a plan specifically for the F-47.
Of course it's also a quote from Trump, so who knows how much of it is from his random sentence generator. Although I'd guess he's quoting another official or someone from the defence industry.
[1] https://www.politico.com/news/2025/03/21/trump-boeing-stealt...
[2] https://www.usnews.com/news/national-news/articles/2025-03-2...
The exact transcript is here:
[3] https://rollcall.com/factbase/trump/transcript/donald-trump-...
All of these are in the top-10 first results when you search for this.