Info needed about PU12 transaction

Hi,

I am making modifications in a User Exit which is providing data to a file defined for Interface format ZTE1 through tcode PU12 interface toolbox.

So, my question is what is this tcode used for ?

And if my changes include making modifications to the file structure by including extra fields and deleting some,what are necessary steps i need to do to ensure same changes are reflected on PU12 side.

I hope my question is clear.

Ask me in case of any doubts.

Please Guide!!!

Answers will be rewarded.

Regards,

Rohan