What I recommend you to do is what most of us DIY hard disk swappers usually do - swap the hard disk, but keep the old hard disk somewhere safe.
Thus, if your notebook goes down, and you are worried about the warranty validity if you return to Toshiba tech support, just swap the old hard disk back, and deny with feigned ignorance ("you mean the hard disk can be changed??" + incredulous looks) to whichever nasty tech support you are not likely to face.
However, most notebook manufacturers do not have such draconian policies, though I have known a couple or two who have tried to charge for repairs, using the excuse that the harddisk/memory has been changed (sly tactics). A bit of force and S.O.B customer attitude should resolve that.