> To start off, I just need to convert true to 's'. false will have to be > manually changed to 'f' or 'p' or 'e' as appropriate.
Second, if you need to display to the user something other than 't' and 'f' that should be done with your UI, not by changing postgres.
Actually, given that "f" is becoming multiple different values it seems like the OP is improving upon their data model. That should very much be done at the table level at not relegated to views, let alone a UI layer.
It is not unusual to want to convert something that was a simple boolean to an enumeration of values. Though it is probably better to add a new column to reflect the new model element and effectively deprecate the old column - eventually removing it from use when it is no longer needed. Altering the column type, while possible, is not usually desirable. In particular it makes rolling back (or supporting older) client software more difficult because the old version will not recognize the new field and the old field will be gone.