Mark and replace strings from my input file

Hello,

I have an input file. Its a .txt-File. From this input .txt File i get my data for my matlab calculation. Is it possible that i mark my sigma_x or sigma_m in my input .txt File with a underline _ or * or something else so i can replace this sigma_x in my matlab Code with \sigma_{x}. I hope you understand what i mean. Thank you for your help.

For example this "r_diagramheaderSigmaX=Rainflow-Matrix sigma_x" in my input

********************Plot Page Options and Settings****** 
pageheader=dummy0 

*******************Diagram Options SigmaX************ 
r_diagramheaderSigmaX=Rainflow-Matrix sigma_x
r_labelordinateSigmaX=Amplitude sigma_a 
r_labelabscissaSigmaX=Mittelwert sigma_m 
r_abscissaMinSigmaX=8.6625 
r_abscissaMaxSigmaX=28.4625

This is my Code:

r_inputdataSigmaX=[;]; 
r_inputdataSigmaY=[;]; 
r_inputdataTau=[;]; 
w_inputdataTau=[;]; 
w_inputdataSigmaY=[;]; 
w_inputdataSigmaX=[;]; 
cuttofflinesSigmaX=[;]; 
cuttofflinesSigmaY=[;]; 
cuttofflinesTau=[;]; 
r_inputdata_logic=zeros(1,3); 
w_inputdata_logic=zeros(1,3);%[0;0;0]; %zeros(m,n) 
inputdata_cuttofflines_logic=zeros(1,3);%[0;0;0]; 
default_value_z=1e8; %hier setze defaultmässig die z Komponente/Wert der Cutofflinien 
row1=0; 
row2=0; 
row3=0; 
index_counter=1; 
t=0; 

%Einlese Prozedere 
wholecontent = fileread('MatlabExport_2.txt') 
sections = regexp(wholecontent, '\*+([^*]+)\*+([^*]+)', 'tokens') 
for section = sections 
   switch(strtrim(section{1}{1})) 
        case 'Plot Page Options and Settings' 
          keyvalues = regexp(section{1}{2}, '([^\n\r=]+)=([^\n\r=]+)', 'tokens') 
          plotpageSettings = cell2table(vertcat(keyvalues{:}), 'VariableNames', {'Key', 'Value'})       
       %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
       %%Die Diagram Options gelten jeweils für rainflow und woehler 
       case 'Diagram Options SigmaX' 
          keyvalues = regexp(section{1}{2}, '([^\n\r=]+)=([^\n\r=]+)', 'tokens') 
          diagramoptionsSigmaX = cell2table(vertcat(keyvalues{:}), 'VariableNames', {'Key', 'Value'})     
       case 'Diagram Options SigmaY' 
          keyvalues = regexp(section{1}{2}, '([^\n\r=]+)=([^\n\r=]+)', 'tokens') 
          diagramoptionsSigmaY = cell2table(vertcat(keyvalues{:}), 'VariableNames', {'Key', 'Value'}) 
        case 'Diagram Options Tau' 
          keyvalues = regexp(section{1}{2}, '([^\n\r=]+)=([^\n\r=]+)', 'tokens') 
          diagramoptionsTau = cell2table(vertcat(keyvalues{:}), 'VariableNames', {'Key', 'Value'}) 
       %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
       case 'Woehler Lines SigmaX' 
          keyvalues = regexp(section{1}{2}, '([^\n\r=]+)=([^\n\r=]+)', 'tokens') 
          w_diagramoptionsSigmaX = cell2table(vertcat(keyvalues{:}), 'VariableNames', {'Key', 'Value'}) 
          w_inputdata_logic(1,1) = 1; 
       case 'Woehler Lines SigmaY' 
          keyvalues = regexp(section{1}{2}, '([^\n\r=]+)=([^\n\r=]+)', 'tokens') 
          w_diagramoptionsSigmaY = cell2table(vertcat(keyvalues{:}), 'VariableNames', {'Key', 'Value'}) 
          w_inputdata_logic(1,2) = 1; 
        case 'Woehler Lines Tau' 
          keyvalues = regexp(section{1}{2}, '([^\n\r=]+)=([^\n\r=]+)', 'tokens') 
          w_diagramoptionsTau = cell2table(vertcat(keyvalues{:}), 'VariableNames', {'Key', 'Value'}) 
          w_inputdata_logic(1,3) = 1; 
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
       case 'Rainflow Options SigmaX' 
          keyvalues = regexp(section{1}{2}, '([^\n\r=]+)=([^\n\r=]+)', 'tokens') 
          r_diagramoptionsSigmaX = cell2table(vertcat(keyvalues{:}), 'VariableNames', {'Key', 'Value'})     
       case 'Rainflow Options SigmaY' 
          keyvalues = regexp(section{1}{2}, '([^\n\r=]+)=([^\n\r=]+)', 'tokens') 
          r_diagramoptionsSigmaY = cell2table(vertcat(keyvalues{:}), 'VariableNames', {'Key', 'Value'}) 
       case 'Rainflow Options Tau' 
          keyvalues = regexp(section{1}{2}, '([^\n\r=]+)=([^\n\r=]+)', 'tokens') 
          r_diagramoptionsTau = cell2table(vertcat(keyvalues{:}), 'VariableNames', {'Key', 'Value'}) 
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
       case 'Rainflow Cutofflines SigmaX' 
          cuttofflinesSigmaX = cell2mat(textscan(section{1}{2}, '%f%f', 'HeaderLines', 1)) 
          inputdata_cuttofflines_logic(1,1) = 1; 
       case 'Rainflow Cutofflines SigmaY' 
          cuttofflinesSigmaY = cell2mat(textscan(section{1}{2}, '%f%f', 'HeaderLines', 1)) 
          inputdata_cuttofflines_logic(1,2) = 1; 
       case 'Rainflow Cutofflines Tau' 
          cuttofflinesTau = cell2mat(textscan(section{1}{2}, '%f%f', 'HeaderLines', 1)) 
          inputdata_cuttofflines_logic(1,3) = 1; 
         %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
       case 'StressSpectrum Data SigmaX' 
            w_inputdataSigmaX = cell2mat(textscan(section{1}{2}, '%f%f', 'HeaderLines', 1)) 
       case 'StressSpectrum Data SigmaY' 
            w_inputdataSigmaY = cell2mat(textscan(section{1}{2}, '%f%f', 'HeaderLines', 1)) 
       case 'StressSpectrum Data Tau' 
            w_inputdataTau = cell2mat(textscan(section{1}{2}, '%f%f', 'HeaderLines', 1)) 
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
      case 'Rainflow Data SigmaX' 
            r_inputdataSigmaX = cell2mat(textscan(section{1}{2}, '%f%f%f', 'HeaderLines', 1)) 
            r_inputdata_logic(1,1) = 1; 
      case 'Rainflow Data SigmaY' 
            r_inputdataSigmaY = cell2mat(textscan(section{1}{2}, '%f%f%f', 'HeaderLines', 1)) 
            r_inputdata_logic(1,2) = 1; 
      case 'Rainflow Data Tau' 
            r_inputdataTau = cell2mat(textscan(section{1}{2}, '%f%f%f', 'HeaderLines', 1)) 
            r_inputdata_logic(1,3) = 1; 
       otherwise 
          warning('Unknown section ERROR: %s', section{1}{1})   

     end 
  end 
  diagramheader=diagramoptionsSigmaX.Value(strcmp(diagramoptionsSigmaX.Key, 'r_diagramheaderSigmaX')) 
  labelabscissa=diagramoptionsSigmaX.Value(strcmp(diagramoptionsSigmaX.Key, 'r_labelabscissaSigmaX')) 
  labelordinate=diagramoptionsSigmaX.Value(strcmp(diagramoptionsSigmaX.Key, 'r_labelordinateSigmaX'))