I have noticed that yes Jalapeno Peppers do get hotter and hotter if you freeze them and the longer you keep the Jalapeno Peppers in the freezer the hotter they seem to get.
That is also true if you let the Jalapenos age more as they get hotter the drier they get and I believe that freezing the Jalapenos also dries them out and causes the peppers to get hotter as a result.
I'm not entirely sure though if that's the reason the frozen Jalapeno Peppers get hotter but I do know in my own personal experience the Jalapeno Peppers do indeed become hotter when you freeze them.
So if you leave the Jalapeno Peppers in the freezer for 6 months or longer be prepared to have a hotter Jalapeno Pepper when you thaw them out and eat them.