He, many things can go wrong, but the more tricky operation is actually the fitting.
We've played on a few cars with removal and fitting ourselves, it is best left to a professional (more on this later) but for removal with some patience, much care and some tools, it is not an impossible task.
You need the wire, use the handles or also a couple of screwdrivers are fine. You need an assistant, the screen is large.
Usually they are bonded with good strong silicon, so a lot of hacking is needed. Plan for at least 30min to an hour of work only in that.
For prep work, in the P38 you need to remove all the trims, the two lateral ones (by the A-pillar) are held in place by screws hidden in the rubber. Once exposed, there are acrobatics with door open at various degrees to get them at. For the lower ones you might find the mirror is in the way, so take screwdrivers of different sizes.
The bottom one looks plasticky, but it actually has a metal insert that keeps the shape. It is held in place by small clips that fit in preselected holes in the ... cabin filter covers and the central cowling.
If the one in the breaker looks mint, get it as well, is a NLA part and always pays to have a nice one. Collect all the clips you can find, if your car had a replacement screen made in the past, you will have a few missing surely!
The top one according to the workshop manual has some slotted pins, mine was silicon glued (bastards) after replacement so cannot help there, never seen how it goes.
From the inside the dash will bother, but if you cannot remove it, that is. If the liner is good to save go VERY carefully around there, because the wire can cut it in fast and easily.
Once you ready, and identified where the heating wires (if any) are - don't cut them with the wire lol!
Set a point where you start - usually a corner - , get the wire in, and start hacking away at a shallow angle. Not too fast, not too slow. You feel the way the wire cuts through and move accordingly. Many position changes might be needed. Don't rush and don't pull, the glass is very ... sensitive by the borders. One chink and the screen is history in a handful of seconds (ask me how I know).
For installation, the glass needs to be very well cleaned and degreased, and you need a specific type silicon (for glass) which is not the normal stuff. It is not expensive, but it has to be the right things. Depending on the age and condition of your car, you might need some sort of primer to add. The silicon needs also a very good pistol, and a dedicated angle of apply. If you are not experienced or don't feel it ... don't. We've tried a couple of times and while we did manage, it is much more hassle than worth hiring a specialist to fit it.
The problem - REAL problem - is that you need to make sure the "specialist" has a clue on how the screen goes fitted to YOUR specific vehicle! Too high or too low, too far out or too in, and you are condemned to a lifetime of wind noise.
Read the section in the workshop manual and make sure that - kindly - you get a feel if the "pro" has a clue about it.
We use a fitter with more than 25 yrs in the business, we've fitted with him more than 30 screens to the same make and model car, so we've been around in where it goes, and yet there is a screw up here and there still ... so beware!
My own P38 has an ill-fitted screen and I have access to a good replacement, but I won't touch until I find someone that knows how exactly it goes in.