Would drilling out the center of the extension minimise the dimensional change?
Maybe, maybe not. It all depends on how the grain lies in relationship to the wood. It could grow inwards, or shrink inwards or the other way around.
As far as epoxy, I use Tite Bond 11 or 111 in a lot of wood working projects, the later being a more water proof/resistant type glue. I have purposely broken some glued up wood either end to end or edge to edge and have never had one break on the glue joint.
Some expoxies are tinted and have a thicker consistancy then wood glues and you will see a marked difference in the joint.
