I figured this out last night and tried it a couple of times.
When the HO wheel comes up, look in the lower right hand corner of it. Sometimes there will be a green coin there. If it is there, that means that the HO is changable.
Then if you use one of your skills associated with the coin icon, the HO will change.
I right clicked on all my skills and examined them to find the ones that were associated with the coin icon. They won't flash when the HO comes up, you just have to know which ones they are.
Hope this helps