That answers nothing, there is no visual feedback, I am PRETTY SURE I am way past stage 10 but I see no way to use them. Do you maybe mean that you need to select them DIRECTLY after doing either ascension or rebirth, or both? The way it is written implies that you can do it at ANY point after reaching these two gameplay elements.
For the record, I did just try it and it worked, but I was not given the info to come to that conclusion in the help text.