The text in Dual Path is controversial. The statement “Select a mythic path other than the path you selected at your moment of ascension.” is used to identify the path that you selected when you ascended, but many players read this as you can only take the Dual Path feat at the moment of ascension.
The Prerequisite also isn’t clear. Anyone that ascends has the 1st mythic tier, so anyone mythic qualifies; however, some believe that this references the only time at which you can take this feat.
As written, there is nothing stopping a player from taking this feat again to get a 3rd path or more.
Additionally, it looks like the 10th level feature in the newly selected path isn’t gained, so you may want to spell that out whichever way you intended it.
There are questions on what tier the feature and abilities of the new path function at. Since there is nothing stating anywhere that you need to keep track of another tier for the new path, I assume that they function at the only tier you have.
Magik