Shower screen fitting

Yes on a 800 side screen if reversed will open right to left or left to right. Once reversed slider fittings are reversed external to internal

Not advisable once finished and sometimes not possible depending on manufacturer.

Once the sliding door is fitted if the door can be disconnected from the running track the fixed glass panel would need to be moved which means dismantling any stops they have used to fit and hold the glass. The only other way would be as in the previous answer flip the door round but this would mean needing to remove the door from where it is fitted to

Once fitted, I wouldn’t risk trying to reverse it as it means removing all the parts and reassembling them. You would have to remove any old silicone and ensure that everything goes back to get her correctly before re dealing with fresh silicone.