Hi Amit,
Sorry for misinterpreting your other thread which is the same to this.

Anyway,
I doubt if you can just disable the constraints, I believe you need to drop it and then recreate it after you have successfully recreate the table with the desired data type.

Assume table orig_tab:
field1 number(2)
field2 varchar2(40)

Table you wanted to be new_tab:
field1 varchar2(4)
field2 varchar2(40)


Here's what I usually do:
1. extract the script to recreate the constraints, then drop the constraints.
2. create the table NEW_TAB with the desired data type.
3. populate the NEW_TAB from ORIG_TAB table:
insert into NEW_TAB select to_char(field1), field2 from ORIG_TAB;
4. check if the same records counts for both table.
5. drop the orig table.
6. recreate the ORIG_TAB table by duplicating the NEW_TAB
create table ORIG_TAB as select * from NEW_TAB;
7. then, recreate the constraints.

Hope this time it can help.

rey :-))