I would better understand this fundamentally if auxiliary parameters weren’t already accepted for ups.conf and upsd.conf
The format of upsmon.conf is the same XDG/INI like format as the other two, so if those aleady have extensive handling to forcefully override some of the values that users place there with specific ones to keep the system from breaking, sanitize user input, etc, that handling should already be abstracted in order to cleanly apply to both and adding a third configuration file that pertains to the same utility shouldn’t be that complicated.
I can understand the reluctance to add more since I know these blanketed “user-append” fields are something that feel ugly and that you’d prefer to do without entriely, but IMO they’re simply a necessary evil.
If I may play devils advocate for a moment:
Having full auxiliary entries for this file allows anyone who needs them to make the changes they need, whereas DEADTIME only helps my particular case. If adding that one parameter is really so much more preferable that its likely to be added, how long until nearly every parameter in all three if these files is in the UI due to one-offs like this? If the auxiliary fields are such a pain, why do the other two exist in the fiest place? Why not just remove them and tell everyone “you can just use a pre-init script”?
Still, if you insist (and I recognize that the other two files are more likely to need user modification than upsmon.conf, ill make a separate suggestion specifically for DEADTIME.