Since it seems like you want constants accessible from a number of applications, why not create a package of constants and start each application by calling the constants you need. You would then change the constants only in the package should they ever need changing.

        (* Mathematica Package *)
    
        BeginPackage["CONSTANTS`"]
        (* Exported symbols added here with SymbolName::usage *)  
        
        constant1::usage = "some text"
        constant2::usage = "some text"
        constant3::usage = "some text"
        
        Begin["`Private`"] (* Begin Private Context *) 
        
        constant1[]: = 22;
        constant2[]: = "myConstant";
        constant3[]: = 0.618;
        
        End[] (* End Private Context *)
        
        EndPackage[]

See: [Package development][1]
Place package in an appropriate directory so Mathematica can see it.

To give your notebooks access to the constants:

   

    Needs["CONSTANTS`"]
    
    constant1[]
    constant2[]
    constant3[]
    
    22
    "myConstant"
    0.618

Just a sketch but this should give you the idea.

  [1]: http://reference.wolfram.com/mathematica/guide/PackageDevelopment.html