Exemption depends on your diploma cert, how many modules you
studied and whether you have enough credits to offset. The
exemption period varies from UNI to UNI. Some uni may allow
exemption from 1 semester to 2 years. It's much better to
check with the uni you are targeting.
But of course, my advise is to focus on your poly studies right
now. A little pointless to worry about what happens after you
graduate with a Diploma, as the Tertiary Education landscape keeps
changing.
Study hard, do well, get a high GPA score and aim for either a
local or overseas Scholarship. With good grades and high GPA score,
you don't need to worry about placement in uni ^.^
My 2 cents