Yes, it worked, once I remembered to put quotes(") round the CASE statement. Thanks again for your valuable input.

Finally:-

Code:
LOAD DATA
INFILE 'z:\PREVIOUS_ADDRESS.dat'
TRUNCATE INTO TABLE PREVIOUS_ADDRESS
(YOUR_COL  POSITION(001:004)  INTEGER EXTERNAL  "CASE WHEN :YOUR_COL = 9999 
                                                            THEN 9999
                                                            ELSE 12*trunc(:YOUR_COL/100) + mod(:YOUR_COL,100)
                                                            END",
 PA_INCOME        POSITION(005:019)  CHAR                
)