[TYPO3-english] writing a function, which gets called at the very last of page rendering

[Domi]

Hello,

I try for setting up a little function, what should get called at the 
end of the whole TYPO3 page rendering. I want to manipulate some 
additionalHeaderData and not sure how to get it running, at this stage 
my function just get called somewhere in the middle.

Any hint appreciated

Cheers
Dominic