OK, here’s the info you asked for.
The studs themselves are 43.5mm long, the threaded section is 25.5mm of this length - both front and rear. Here endeth the good news.
On the front, there simply is not room to drift the studs out. It looks like they are fitted to the hub during the assembly process and once fitted, there is a circular slotted collar behind the plate the studs mount through which means there is not enough room to get them out:
This is the front passenger side hub, you can see that the studs are about twice as long as the void behind the stud mounting plate and the slotted plate/backing plate - so you’d not have enough room to get the OE studs out, and certainly not enough room to get even longer ones in without splitting the hub. It could be done, but will be a major job requiring a puller and a press at the very least.
I didn’t bother getting the rear drum off once I’d seen this, I expect that its a similar story there though, with needing to remove the hub nut & brake drum, brake pads and cylinder, split the hubs with a puller, drift the studs out, fit the new studs and use a press to re-attach the hub assembly.
There might be a way around this, but my garage is freezing currently and I don’t get much lunchbreak from work so this is as far as I could go. One option might be to get a full set of secondhand hubs and split them, sort the new studs etc etc on the bench, then fit them to the car - but having stripped down and rebuilt the front hubs a few times on my M1 Sirion its not a quick job, and WILL immobilise the car if you strip a thread or break something (as me how I know…)
There might be such a thing as a threaded stud extender collar you could screw onto the factory studs, then wind another bit of threaded bar onto the end of, but even if it does exist it sounds dodgy AF and no way would I use them