Yes, you could programme each junction event's Audio and Video source (actually think it was labelled as Sound and Vision) and the transition (cut, mix, wipe) into the memory. You entered them into the memory in the order the junction would occur, and if you made a mistake you had to clear the whole memory and start again... which was really annoying if you were entering every event in the junction into a local news bulletin, every event in the news you were directing, and every event in the junction after the news. It was very easy to lose your place. Fortunately you could enter memory rehearse mode and try the whole sequence out to make sure it was all there.
I can see how the lack of memory edit would've been very frustrating at times. At 9.23pm (weekdays), You probably didn't want to hear the network director say they had to completely rejig the 9.30pm junction!
What you had to remember to do of course, was to come out of memory rehearse before the actual junction... otherwise the viewers at home wouldn't see the junction, and you'd be doing the whole thing for no one but yourself!
Yes, well, I think I can say I've possibly seen the result of that at least once, in its early days in use. My suspicion at the time was that the desk somehow got "locked up". However, the announcer/director sitting in rehearse mode seems the more likely explanation. The situation was the 6.30pm repeat of 'Neighbours' (NI put out their regional news at 5.35pm in those days). BBC NI usually just recorded the 1.30pm episode off the network feed (which back in those days contained all the network continuity) and replayed that at 6.30pm. So, 'Neighbours' was introduced as usual at 6.30pm and played out fine. But when the programme ended, rather than getting the 'Inside Ulster Update', just before the 7pm programme (probably 'Wogan'), we got the 1.50pm junction and the start of the cricket coverage that went out at lunchtime. I can't recall if we ever joined the local news update or crashed back to network eventually (I suspect the latter). I know the tape played on for ages.