[Exim] Debian packages?

I would like to create my own Exim-deb to include a few features. Soo, now the question is, does someone have some details on how i could use the existing source-deb to add these features? And of cource, would i be stepping on anyones toes/work if i did that?

My plan is to create a deb that docks with XAMS, sinc ei am startin gto like that tool.

regards, Jan.