halfdome:
Of course one could iterate over each character in the array, but isn't there some better way?
Your char array is a string, C-string or zero terminated string.
You can use all the string functions with it.
A new value can be assigned to the string this way:
if (HIGH==HIGH) strcpy(char_array,"ABCD");
Be sure not to assign a string that is longer than the declared one, or you will overwrite RAM memory that belongs to different variables defined in your sketch.