Yea this is done all the time.
I will find out all the regulations for you ASAP.
I do know that you have to get it weighed also.
You now need to get an engineers report to state it has been done according to the Laws.
You need get rid of the back seats and put at a flat floor in.
And yea I have heard of people getting away with just tinting the rear windows
Now when I think of this I am surprised not many Glanza's / GT's have been converted to vans in Ireland for the big savings on Tax and Insurance
And YES IT IS LEGAL.