QlikView will always decide the number formatting of a field the first time this field is loaded. So because of the facts that:
1) QlikView has identified this fieldname with the NUM-format when it first loaded this field.
2) you are reusing this fieldname.
; QlikView will use the NUM-format as the default format for your dual-value. This also explains that when you give the field another name, it does use the TEXT-format as default (as it usually does with dual-values).
Not sure about that one, I don't think this is possible. You can however use a renamed field as the inputfield for your applymap.
tt_EntryType as EntryTypeCode,
dual(ApplyMap('EntryTypeMap', tt_EntryType), tt_EntryType) as [Entry Type]
DROP FIELD tt_EntryType FROM ItemLedgerEntry;
Offcourse this implicates that you do a rename to tt_EntryType on your original load.