I have modified your file1.m, for the function to take input arguements. Because of this you'll need to change how you are calling the "params" function. ie by passing the default values.
p = params();
p = params(2,5)
So, your file2.m, file3.m and file4.m will require changes as above.
Your file1.m now looks like this:
function out = params(m,n)
out.mu1c = -(1./2).*n-(1./2).*m+3./2 ;
out.nu1c = (1./2).*n+(1./2).*m+1./2 ;
Now because of the change made in file1.m, it will help you in acheiving what you want in file4.m by just passing the input arguements ie different values of 'm' and for same values of "n"
p = params(i, 5);
If you want to learn more about default values for input arguments for a matlab function, please check out
I would suggest you to take the free Matlab OnRamp course which will bring you up to speed with the Matlab language.