[Kanegasi]

Ah, I missed that. The taint source for that is at the bottom.

frame.DefaultAddMessage = frame.AddMessage --idk what all of this is
frame.AddMessage = AddMessage --idk what all of this is

As for the things you do in your replaced AddMessage, you already use ChatFrame_AddMessageEventFilter for some events. For the stuff you can't change through the filter return, just build your own message and feed it directly into AddMessage, then return true in the filter so that the original line is filtered. The event filters get all the returns from the chat event, so you can do anything Blizzard's chat output does without replacing AddMessage.

Here's an example of your channel header change added to colorName along with duplicate protection. Keep in mind I did not test this, but this should give you an idea to go on whether it works or not.

local messages={}
local function colorName(self, event, msg, ...)
 
    local test = msg:gsub('[^a-zA-Z%s]', '')
    local words = {strsplit(' ', test)}
    for i = 1, #words do
        local w = words[i]
        if (w and not (w == 'player' or w == 'target') and UnitName(w) and UnitIsPlayer(w)) then
            local class = select(2, UnitClass(w))
            local colors = RAID_CLASS_COLORS[class]
            if (colors) then
                msg = gsub(msg, w, '|cff'..RGBPercToHex(colors.r, colors.g, colors.b)..'%1|r')
            end
        end
    end
 
    -- get some of the args from the chat event
    local namerealm,lang,fullchan,name,afkdnd,zoneID,chanID,channame,unusedzero,lineID,playerguid=...
 
    -- get text color and id of event (FrameXML\ChatFrame.lua:3186)
    local type = strsub(event, 10)
    local info = ChatTypeInfo[type]
 
    if event=="CHAT_MSG_CHANNEL" then
 
        -- prevent duplicate messages
        if messages[lineID] then
            return true -- hide, do nothing
        else
            messages[lineID]=true
        end
 
         -- since we have the raw message, we have to add the channel number ourselves
        msg = "|Hchannel:channel:"..chanID.."|h"..chanID..".|h "..msg
 
        -- we also need to add the timestamp exactly how Blizzard does it
        -- FrameXML\ChatFrame.lua:3540 (BetterDate @ FrameXML\UIParent.lua:4736)
        if CHAT_TIMESTAMP_FORMAT then
            msg= BetterDate(CHAT_TIMESTAMP_FORMAT, time())..msg
        end
 
         -- add message as if it was the original
        self:AddMessage(msg,info.r,info.g,info.b,info.id)
 
         -- hide original message
        return true
 
    end
 
    return false, msg, ...
end