Make all new cells have a specific style as a function of the Mathematica installation

Question

I would like all new Input and Output cells, in fact all new cells including section headers and such, to have a specific stylistic property (CellBracketOptions -> {"Color" -> MyFavoriteColor}).

This is easy enough to do with CurrentValue[$FrontEnd,...]=.... However, I want this behavior to be exhibited only by new cells created in a specific *Mathematica** installation. I.e. a notebook generated elsewhere should look like it would in a default Mathematica FrontEnd, and only new cells created in this Mathematica installation should have the new property.

My use case here is that I have a notebook that I would like to use for collaborations, where each person would be assigned a color, and when they use their copy of Mathematica the cells they enter would automatically have a distinctly colored cell bracket. When exchanging this notebook, the cells authored by each user would be readily identifiable by their cell bracket color.

Answer 1

This is how you can customize given notebook. Needs some testing but seems to work.

It distinguishes users based on $UserName but you can use $MachineID or whatever.

CurrentValue[ EvaluationNotebook[], {TaggingRules, "Collaborators"}] = {
   "Kuba" -> Orange, "Friend" -> Red};

SetOptions[
  EvaluationNotebook[], 
  CellDynamicExpression :> Refresh[
    With[{col = CurrentValue[EvaluationNotebook[], {TaggingRules, "Collaborators"}]}
      ,
      If[
        MemberQ[First /@ col, $UserName]
        ,
        RunScheduledTask[
          SetOptions[#, CellDynamicExpression -> None];
          CurrentValue[#, {CellBracketOptions, "Color"}] = ($UserName /. col)
              , 
              {.2}
        ] &@EvaluationCell[]
 ]], None]]