Here's a trigger to turn this:

Into this:

To turn on kill assists in deathsight, use CONFIG SEEASSISTS ON.
Create a new colour trigger, set to fire on the colour of your deathsight lines. (CONFIG COLOR will give you the ANSI colour code.)
ds = ds or {}
if ds[1] and (not ds[2]) then
local g = getCurrentLine()
if g:sub(1, 17) == "Kill assisted by " then
deleteLine()
cecho(' <light_sea_green>(assisted by '..g:match("%d+")..')')
end
ds[2] = true
elseif (not ds[2]) then
ds[1] = true
end
if ds.t then killTrigger(ds.t) end
ds.t = tempPromptTrigger([[
ds[1] = false
ds[2] = false
ds.t = nil
]], 1)
Comments
General - https://github.com/27theo/achaea
Limbs - https://github.com/27theo/limb
Char DB - https://github.com/27theo/cdb
Can't say I'm fond of how it looks by default (using the word "kill" in this fashion seems a bit too much like game-language to me and feels slightly immersion breaking), so I certainly prefer your variant.
→My Mudlet Scripts