Staging User Data in a Table - Lua

So I have an idea, but upon initial thought it seems like a bad one. I'd like to store UserData for the life of the script in an external table (called by require).

I'm looking for ways to implement this, but I'm thinking that storing UserData in a global environment could be troublesome. Could someone point out any pitfalls from this method? Or provide a better suggestion?

External (centralized) function - loaded using 'require' during script execution:

--Chat.lua
--Location: Scripts/Globals/Custom/Functions/Chat

Convo    = 0xD
Special  = 0x1F

TempUserData = {}
TempTargetData = {}

function Show (Message, Display, Color, VAR1, VAR2, VAR3, VAR4, VAR5)

    local User = TempUserData[1]
    local Name = Display and TempTargetData[1]..":  " or "  "
    Color = Color or Convo
    VAR1  = VAR1  or nil
    VAR2  = VAR2  or nil
    VAR3  = VAR3  or nil
    VAR4  = VAR4  or nil
    VAR5  = VAR6  or nil

    if (VAR1) then
        User:PrintToUser(string.format(Name..Message, VAR1, VAR2, VAR3, VAR4, VAR5), Color)
    else
        User:PrintToUser(Name..Message, Color)
    end

end

Main script:

---------------------------------------------------------------
package.loaded["Scripts/Globals/Custom/Functions/Chat"] = nil
require("Scripts/Globals/Custom/Functions/Chat")
---------------------------------------------------------------

local function foo (VAR1)

    Show("Message")
    Show("Message",true,Special,VAR1)
    --Stuff

end

local function bar (VAR2)

    Show("Message")
    Show("Message",true,Special,VAR2)
    --Stuff

end

function onTrigger (User, VAR1, VAR2, VAR3) --Start of script

    table.insert(TempUserData, User)
    table.insert(TempTargetData, "System")
    --Stuff

end

The reason I'd like to do this is because:

1. User:PrintToUser is not my function. It could change at some point or be renamed and since I have so many files using it, changing it in one location and having the effect cascade to my own custom scripts is appealing to me.

2. Some messages can be lengthy and having User and Target in-line with the function call is just more space added over and over.

3. The end result is shorter and cleaner, thus making it more readable in a large script. Also, make debugging easier for me (how many times I've misspelled PrintToUser as printToUser...)

Instead of:

User:PrintToUser(string.format("Message %s, %s", VAR1, VAR2), 0xD)

It could be cleaner:

Show("Message %s, %s", true, Convo, VAR1, VAR2) -- With variables

or

Show("Message",true) -- Display "System" with default color
Show("Message") -- Don't display "System", still with default color

I have two questions regarding this:

1. Based on the code above, would I run into problems if several people are using the same script at once? (i.e. User Data somehow being mixed up, or global variables in use).

2. Would there be any performance degradation from redefining functions in this way? Or from storing, retrieving, deleting a table of User Data each time? (200+ people using this)