SQL & PL/SQL

I know we have to use Execute immediate with DDL if used in a PL/SQL block. or with a variable.

But can I run DDL directly in SQLPLUS or Oracle SQL developer? I think the answer the yes, but just want to confirm.

for example if I do something like below

In Oracle SQL developer:

I make the database connection and open a worksheet, and do the following

ALTER SEQUENCE customers_seq   CACHE 5;

I don't need to use immediate execute if I don' put it in a  PL SQL block, correct?

And it is an implicit commit?

Thanks