[James2001]

On that video, the switch occurs at the end of an ad break, so there wouldn't have been any sort of glitch or interuption to the show itself. How it was handled in terms of playout though, I don't know, was the whole thing played out by either GMTV or STV and just routed through the other, or were the pre and post 9:25 segments played out from different places? Likely the former, the latter feels like it would be ridiculously convoluted, but there's no way of telling just from the video.

The Friday episode of Home and Away was a show that straddled the Thames/LWT switch as well (though by the back end of 1992 it seems to have moved after the early evening news rather than before it, so entirely within LWT), I'm pretty sure in that case it was played out by Thames and routed through LWT- and the switch did happen mid show, not during a break.