Is There a Way To Use a Single Item Inside of a Variable?

Maybe from the title you didn’t understand but what I mean is there a way to take for example this variable

Test = Var1 Var2 Var3 Var4

I need to take this variable and use it in some post data using it like this

Test=Var1+Var2&Test2=Var3&Test3=Var4

Functions → Constants