Yes, the implementation of DM into XR is quite final (not with the very final balancing changes as far as I remember though. Things like in XR hitting an NPC gives a 3 second speed boost and in my mod I changed it to 1 second.):
What you need though is to load a proper DM map:
Some people laughed at me in the past that I don't usually throw digital things away, nor does anything important ever get lost (except the passwords in the server and startup.cfg of course). Well, here's the SFE+ linux server created by Sweet back in 2007 with the final deathmatch mod running on it created by me. All maps and configs are included, even a full map history.https://drive.google.com/open?id=12Jb136bN4Xguh6murGA9G-r17lUC5lvM
While we're at it... Instagib unfortunately never made it to Savage XR. So, here's the latest Instagib server running on SFE:https://drive.google.com/open?id=1M8I014z_cMbOYdZC9qtQqmSZfbdfGdyt
Remember to change the map URL and the CPU the game server is running on in sfe_dedicated_Sweet.sh
PS: While I'm at it... I'm now going to respond to one of my first e-mails I received back 1998. So much fun!