Edit a number like mass in Nastran .bdf file

Hi all

I want to modify mass parameter in a bdf file using matlab. checking this code but I couldn't edit it in a way to change the 4th column in front of CNOM

fname = 'bpillar.bdf' ;
fid = fopen(fname,'r') ;
S = textscan(fid,'%s','Delimiter','\n');
fclose(fid) ;
S = S{1} ;
%%Get the line number of CBEAM
idxS = strfind(S, 'CBEAM');
idx = find(not(cellfun('isempty', idxS)));
cbeam = S(idx(2:end)) ;
k = cellfun(@strsplit,cbeam,'un',0) ;
iwant = cell2mat(cellfun(@str2double,k,'un',0)) ;

[Stephen23]

@farzad: please upload a sample file by clicking the paperclip button.