I believe the resistor is there to control the charge rate of the original NiCad. (The original charging circuit doesn't seem to have any means of detecting full-charge, but I don't know how important that is in this application.) It's useless when replacing with a coin battery and diode. While leaving it in place does little harm (referring to Castellen's earlier comments), it's a handy place to install the diode, with the benefit of being able to easily solder the 2032 coin socket directly to the board, and potentially a bit longer battery life with a Germanium or (better) Schottky diode.
