Done a bunch of BX60's and 50's, well I say a bunch, maybe a half dozen. Never takes more than 2 hours labor. Pull the motor, it's so easy to do on these. A few wires, 2 hoses, 4 nuts and slip it past the fan shroud, and it's out in 30 minutes or 35 minutes if it's got a loader. Just faster (for me) to do it that way then it is to fight with cutting the fan in half and then fighting those two bolts. Also removing the engine gains access to a nasty area under and behind it that normally you don't see, so you get the opportunity to wash it out good; plus when the shaft is out, you can check the condition of the U-joints. Trust me, from experience, if one of the U-joints comes apart while it's running 3500 RPM, things aren't very pretty. That shaft goes absolutely wild. IMO there should be a loop around it to keep it contained, but again, apparently the engineers thought it was ok; and for the most part it is.
IF the fan were metal, the blades would just bend. Then the possibility exists that whatever bent the blades could be wrapped up in the fan itself, around the shaft, and then create all sorts of problems. OR if a blade broke off, you then have a projectile, possibly come through the floor where your pride and joy are, whether it be your feet or.....
I reckon it's ok to put a skid plate on it, assuming no belly deck. But make sure to vent it properly so that the little fan can get some air. That's all that cools the transaxle and hydraulic fluid, there is no other cooling mechanism.
In most of the ones I've done, after quizzing the operator what they were using the tractor for, usually I am finding that they were using it for something it wasn't designed for, e.g. bulldozer. Clearing land, hopping over trees, etc. I realize that sometimes stuff happens; and if the owner has Kubota's insurance, they'll usually pick up the tab minus the deductible.