SQL & PL/SQL :: How To Make PK Not To Validate

i am writing a script for inserting rows in a table where primary key of that table consists of 4 columns. I want to add a new row where 3 columns of that table will be same but change the value of the last one. this is giving an error saying that i am violating the unique constraint. I tried to disable that constraint/PK by following statement but still this error is coming

alter table sections_budgets modify primary key disable cascade;

OR

alter table sections_budgets modify constraints sec_bdgt_pk disable cascade;

the insert statement which i am using. The first four columns are part of PK

insert into sections_budgets (SELECT sb.bdgt_cd, sb.bdgt_dpf_cd, sb.bdgt_yr, :sec_code, sb.usf_usr_id,
sb.aty, sb.comaty, sb.comytd, sb.expn_ytd, sb.sys_dt, sb.cat,
sb.start_aty, sb.expn_lmt
FROM sections_budgets sb
WHERE sb.bdgt_dpf_cd = :b_d_code AND sb.bdgt_yr = :year);

is there any other way of inserting records in this table without droping the whole table because it contains too many triggers and constraints?