How do I build the modified dvips driver?
As I did not build a modified dvips driver for a long time (there was no need to do so as I have enough disk space available now) I can no longer give detailed recommendations. In “good old times” the current dvips sources were available in the tetex distribution sources on CTAN. I don’t know where to find them today. So I can not derive modified dvips sources from the original. I can only recommend to run a diff command to compare the modified dvips sources in the dvips-mods/595a directory against the original dvips 595a sources to find the changes you have to apply to the dvips sources.