I don't think there is a mechanism for doing adjustments to DKP in game. Keep in mind that when you upload DKP you are not uploading points from the mod back to the site. You are uploading captures of who was present at different points of time during the raid and assigning points to that based on whatever criteria you use.
With that in mind it sounds like you do a negative DKP for late or no show events. I have an alternative for you that might make the manual tracking and adjustments easier. I assume that your making a small impact to DKP for someone that is late and maybe a slightly larger one for someone that didn't show up but signed up and never gave a reason afterwards as to why they didn't make it.
If it were me to make things simple and work in the system I would (and did when I ran my guild and dkp) do the opposite of a DKP minus for late comers. Before the raid starts you set a time for when people will be counted as late. We used to set that time to 5 minutes before the first pull. You had to be in the instance and ready. We did a manual snapshot of the raid and called it OnTime. The nice thing is that is shows you the zone that people are in when you upload it. So the guy that is standing outside at the summoning stone and didn't go into the instance...well he wasn't ontime and ready by my definition so no bonus dkp. Instead of subtracting DKP from those that were late we awarded a 2-5 point bonus to those that were there and ready to go when the rest of the raid was.
No shows - After you do all your uploads for the night you can go and see exactly who signed up and never showed up at all. Currently you would have to do it manually but you could do a manual raid and call it No Show and associated with your calendar event. Then just check off the people that were no shows and your done.
You can actually build things like OnTime and NoShow as manual destinations that can associated with any calendar event either by building a manual raid or importing a raid. The advantage there is that you can assign the point value as a positive or negative value to be awarded for everyone associated with that destination. Personally I have never used a negative point value on a destination but I don't know why it wouldn't work.
We had asked a long time ago for Chops to build into the tracking some mechanisms for this but I think with all the updates for other critical issues it got left behind. So even though I won't use them but others might I'll toss them back out.
1. When uploading a raid event there should be an option to compile a list of people that are not in every snapshot to facilitate awarding a Start to Finish bonus indicating that a person was present for an entire raid.
2. When uploading a raid event there should be an option to compile a list of people that didn't show up at all for any portion of a raid so that guild that do so can add a negative adjustment to those individuals.
An update for the mod. Since GRSS can download event data now it would be really helpful for consistency if some kind of timer/udate mechanism could be added to GRSS so that guilds that want to use OnTime snapshots can have them done automatically at the time a raid is scheduled to start. Having a timer mechanism would also allow for people that want to schedule snapshots every X minutes and award dkp based on time (but that is a stretch).
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Six Demon Bag
Jack Burton: Hey, what more can a guy ask for?
Egg Shen: Oh, a six-demon bag!
Jack Burton: Terrific, a six-demon bag. Sensational. What's in it, Egg?
Egg Shen: Wind, fire, all that kind of thing!
