You can use strfind() to find a pattern within text. So, for example:
A={'asdf,asdf','asdf,asdf,asdf','asdf'}; strfind(A,',')
ans =
[5] [1x2 double] []
I'm sure you can do it with regular expressions as well, but I am not familiar with that. It looks to me like strrep() already does what you want (replace commas in a short time).
If you want to apply a function to a cell array that does not accept cell arrays as input, you can use cellfun() to apply a function to each array in a cell individually.
