Wrapping Query in "select *" changes execution path

Oracle 10.2.0.4
Red Hat 4 x86_64

We have an application that runs standard SQL as a reporting tool. The amount of rows that can be returned is limited by a variable. The application manages this by changing the straight SQL from this:

select *
from users;

into this:

select * from (
select * from users)
where rownum < 25000

This is causing a change in some execution paths.

Is there any (simple) way I can stop or influence this behaviour?

Thanks

Ray

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