While the Vstrom might look built for an Adventure, in reality it’s no more off-roader than most bikes.
Like anything, practice helps.
Even with ABS fitted, I rarely use the front brake in such circumstances (and do so very gently if necessary), I always keep my feet on the pegs, (far better for balance and you’re less likely to damage yourself) and do everything in slow-motion.
It’s no different to riding on frosty winter roads.. slow and steady.
Unless you’re going on an extended off-road ride there’s little point in adjusting tyre pressures, definitely not considering the little stretch you travelled.
I’d take up the offer from the IAM instructor, if nothing else it’ll be a bit of fun, but be aware you’ll be slipping and sliding far more than any ‘proper’ off-roader’. Plus, whether 650 or 1000, they’re a damn sight heavier to pick up if you do slip off. ????