Possible modify cached object HTTP MIME fields?

[ChangCheng]

Hi :
i konw we can retrieve and modify information about HTTP MIME fields by using 
MIME header functions.
i would like to konw can i modify cached object header use these functions?  i 
try to use these method to modify cached object header which get from 
TSHttpTxnCachedRespGet. but it seem to doesn't work. 
Any suggestions?
Thanks