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 Place package in an appropriate director 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.