Anyway, I've done about 20-30 miles this afternoon and evening and can report that the gearchange feels slightly better, a bit less notchy, but otherwise not vastly different from normal.
On Sunday my car sailed through the 75000-mile marker, so this oil change is a preventative measure in the hope that my gearbox does not follow the frightening pattern of failures that seems to be plaguing the country's GTis! There's not much else I can do other than to not rush any gearchanges, and be patient when choosing reverse (which still grumbles).
Happy cog-swapping people!
Cheers