delta AICc between HKY and GTR is 31, and if it is more than 10 it is significant, correct?
Yes, that is what I understood as well after extensive reading, that it does not allow setting a 4 parameter model. What I ended up doing in the end is running my analysis with a Mixed model, which is supposed to try out every possible model, including JC, GTR, etc. I already ran the analysis with GTR, and it looks okay, just want to make sure that the values do not change for branch support when I do the Mixed model.