create table prp (
  prp_name varchar2(1) not null,
  i_name varchar2(1) not null,
  prp_id number(22) not null,
  prp_date date,
  br_prp varchar2(255),
  prp_partner number(22),
  prp_seq_no number(22),
  product_type varchar2(10) not null,
  prp_ref_no varchar2(255) not null,
  m_user varchar2(30) not null,
  prp_comp varchar2(10),
  prp_code varchar2(10),
  first_name varchar2(40),
  prp_dept varchar2(60),
  prp_street varchar2(10)
);

create table tmp_prp (
  product varchar2(10) not null,
  product_type varchar2(10) not null,
  tseq_no number(22) not null,
  ref_no varchar2(255) not null,
  fname varchar2(40),
  lname varchar2(40),
  street varchar2(40)
);
 
Data from customer in xls (I've converted to csv seperated by |). This data is loaded onto tmp_prp table.
 
'Med'|'STR'|45|'HR4'|'Francis'|''|'Main st'
'Medpr'|'STR'|18|'HR9'|'Andrea'|'Nelson'|'Swift Way'
'PharK'|'RKN'|22|'IR2'|'Mary'|''|'Swift Way'

SCOTT@orcl> HOST TYPE test.dat
'Med'|'STR'|45|'HR4'|'Francis'|''|'Main st'
'Medpr'|'STR'|18|'HR9'|'Andrea'|'Nelson'|'Swift Way'
'PharK'|'RKN'|22|'IR2'|'Mary'|''|'Swift Way'

SCOTT@orcl> HOST TYPE test.ctl
LOAD DATA
INTO TABLE tmp_prp
FIELDS TERMINATED BY '|' OPTIONALLY ENCLOSED BY "'" TRAILING NULLCOLS
( product       POSITION(1)
, product_type
, tseq_no
, ref_no
, fname
, lname
, street )
INTO TABLE prp
FIELDS TERMINATED BY '|' OPTIONALLY ENCLOSED BY "'" TRAILING NULLCOLS
( prp_code      POSITION(1)  "NVL (:prp_code, 'PRIN')"
, product_type
, prp_seq_no
, prp_ref_no
, first_name    "CASE WHEN :product_type = 'STR' THEN :first_name ELSE NULL END"
, lname         BOUNDFILLER
, prp_street
, prp_name      CONSTANT 'P'
, i_name        CONSTANT 'I'
, prp_id        CONSTANT  1
, prp_date      SYSDATE
, prp_partner   SEQUENCE
, m_user        CONSTANT 'TST'
, prp_comp      CONSTANT '%'
, prp_dept      "CASE WHEN :product_type='STR' AND :lname IS NOT NULL THEN :first_name||:lname END")

SCOTT@orcl> create table prp (
  2    prp_name varchar2(1) not null,
  3    i_name varchar2(1) not null,
  4    prp_id number(22) not null,
  5    prp_date date,
  6    br_prp varchar2(255),
  7    prp_partner number(22),
  8    prp_seq_no number(22),
  9    product_type varchar2(10) not null,
 10    prp_ref_no varchar2(255) not null,
 11    m_user varchar2(30) not null,
 12    prp_comp varchar2(10),
 13    prp_code varchar2(10),
 14    first_name varchar2(40),
 15    prp_dept varchar2(60),
 16    prp_street varchar2(10)
 17  );

Table created.

SCOTT@orcl> create table tmp_prp (
  2    product varchar2(10) not null,
  3    product_type varchar2(10) not null,
  4    tseq_no number(22) not null,
  5    ref_no varchar2(255) not null,
  6    fname varchar2(40),
  7    lname varchar2(40),
  8    street varchar2(40)
  9  );

Table created.

SCOTT@orcl> HOST SQLLDR scott/tiger CONTROL=test.ctl DATA=test.dat LOG=test.log

SQL*Loader: Release 11.2.0.1.0 - Production on Mon Apr 20 17:58:21 2015

Copyright (c) 1982, 2009, Oracle and/or its affiliates.  All rights reserved.

Commit point reached - logical record count 3

SCOTT@orcl> COLUMN ref_no FORMAT A6
SCOTT@orcl> COLUMN fname  FORMAT A7
SCOTT@orcl> COLUMN lname  FORMAT A6
SCOTT@orcl> COLUMN street FORMAT A9
SCOTT@orcl> SELECT * FROM tmp_prp
  2  /

PRODUCT    PRODUCT_TY    TSEQ_NO REF_NO FNAME   LNAME  STREET
---------- ---------- ---------- ------ ------- ------ ---------
Med        STR                45 HR4    Francis        Main st
Medpr      STR                18 HR9    Andrea  Nelson Swift Way
PharK      RKN                22 IR2    Mary           Swift Way

3 rows selected.

SCOTT@orcl> COLUMN br_prp         FORMAT A6
SCOTT@orcl> COLUMN prp_ref_no FORMAT A10
SCOTT@orcl> COLUMN m_user         FORMAT A6
SCOTT@orcl> COLUMN first_name FORMAT A10
SCOTT@orcl> COLUMN prp_dept   FORMAT A12
SCOTT@orcl> SELECT * FROM prp
  2  /

P I     PRP_ID PRP_DATE        BR_PRP PRP_PARTNER PRP_SEQ_NO PRODUCT_TY PRP_REF_NO M_USER PRP_COMP   PRP_CODE   FIRST_NAME PR
P_DEPT  PRP_STREET
- - ---------- --------------- ------ ----------- ---------- ---------- ---------- ------ ---------- ---------- ---------- --
---------- ----------
P I          1 Mon 20-Apr-2015                  1         45 STR        HR4        TST    %          Med        Francis
        Main st
P I          1 Mon 20-Apr-2015                  2         18 STR        HR9        TST    %          Medpr      Andrea     An
dreaNelson Swift Way
P I          1 Mon 20-Apr-2015                  3         22 RKN        IR2        TST    %          PharK
        Swift Way

3 rows selected.

CREATE SEQUENCE str_seq NOCACHE ORDER
/
CREATE SEQUENCE rkn_seq NOCACHE ORDER
/
CREATE OR REPLACE FUNCTION get_seq
  (p_product_type IN VARCHAR2)
  RETURN             VARCHAR2
AS
BEGIN
  IF p_product_type = 'STR'
    THEN RETURN 'STR' || str_seq.NEXTVAL;
  ELSIF p_product_type = 'RKN'
    THEN RETURN 'RKN' || rkn_seq.NEXTVAL;
  ELSE
    RETURN p_product_type;
  END IF;
END get_seq;
/

m_user  "get_seq (:product_type)"