The HST is not a trim tank like it is on the A330/340. It's just another place to stuff fuel.
That is not to say it won't seriously affect trim. I understand that it's not standard practice to fine tune the balance of a 744 by transferring fuel (manually), but if fuel is to be loaded in the HST, a certain ratio must be maintained between the CWT and the HST prior to takeoff - 6:1? And, if you can't burn fuel from the HST due to a malfunction, then you may end up dangerously out-of-trim.
Cheers.
NSEU