This info is nowhere to be found. Where did you get this impression?
I can immediately say that SP are not what help you rank up. You get XP based on kills, medals, etc. You only get a set amount of SP each time you rank up. See, you earn XP to rank up, and you get SP when you do rank up.
I do not know if you can rank down, but it seems likely that deaths, getting assassinated, etc would TAKE XP. That would be more realistic based on what 343 have shown and said. They stated, "1-50 numbers are not returning."
Therefore, what you have stated seems unlikely.