Of course you can't roll part of a Roth account into a traditional account! I was referring to the TSP policy of taking distributions (traditional or Roth) pro-rata across all investments. So if you have 50% of your TSP (traditional or Roth) in the C fund, 25% in F and 25% in G, and you want to take $10,000 out, they will take $2500 out of the G and sell $2500 worth of shares from the F fund and $5000 from the C fund - you can't direct them to take the whole $10,000 from the G fund.
