find substring that includes variables and generic characters, and replace with new string - problems posing search target

Hello, My name is John and I am having an issue getting regexprep to recognize a series of characters. I have read a text file into a string, and want to find instances of this [var1]([index1]) = [existingvalue] and replace [existingvalue] with [newvalue], resulting in [var1]([index1]) = [newvalue]. E. g. EXNE(5) = 9.38487 with EXNE(5) = 9.3928 or XTE(17) = 9284.19 with XTE(17) = 92.934. The index goes from 1 to 25 for each variable.

     This is the main part, and I want it to do what appears here:
variablenameindex = {'var1','var2','var3','var4',...}
var1valueindex = {5.203, 6.204, 7.839, 9.093,%... to 25
var2valueindex = {7.803, .204, 9.839, 1.093,%...  to 25
%... to 13 variables
variablevalueindex = {var1valueindex,var2valueindex,var3valueindex,...}
for i=1:length(variablenameindex)
    var = variablenameindex(i)
    vector = variablevalueindex(i)
  for j=1:25
     val = vector(j)
     regexprep(fullstring,strcat(var,'(',num2str(j),')',' = ','\d*.\d*'),...        strcat(var,'(',num2str(j),')',' = ',num2str(val))
  end
end

for i = 2 j = 4 for instance, I can't get it to recognize var2(7) = X.XXXX and make it var2(7) = 1.093. Any help would be much appreciated!!! Thanks, john