One way to remap your classes would be to use the Classification ->Post Classification->Combine classes tool.  It sounds like it can only combine classes but you can also 'switch' classes using this tool.  For example, I can select class 1 from the input column and set it to be output to class 3.  Then I can set class 3 from the input to class 1 on output.  This will switch the two classes.  What you can't do is assign it to a new class value that does not exist.  If you wanted to do something like this, you would have to use something like Band Math to manually change values to new values not already contained in the data.