A high yield fund is like investing in stocks. That is, one might consider it 20% or 30% stocks and only 70% or 80% bonds. So if you want that, just take 20-30% of your GNMA fund and buy a stock index fund.
It's funny that you mentioned munis because they "popped" after the election, but have a negative performance since December 07 when they dropped about 1.5% in 10 days because of rumors that their dividends might be taxed. They have since recovered to a 0.5% loss when the new tax laws didn't change that.
The 3-month returns of intermediate bonds is flat, so I don't see what you are saying about GNMA funds. Since they are guaranteed as to payment of interest and principal, one can consider them easily Treasury bonds. In today's low interest rate environment, GNMAs are doing exactly what they should be doing.
If you wish to chase yield and safety, then you are probably better in CDs right now. If you wish to chase yield and don't care about safety, then by all means jump into high-yield bonds, but I myself would just up my equity allocation if I wanted to chase performance.
If you want to chase yield with a little bit of safety, you can do corporate bonds and stay with short-term durations.
In essence, there is no place to hide nowadays in bond funds. Every choice you make is not like a choice you could've made a few years ago.
Hope this helps.