Hmmm. You’re on the right path, need to get that cover off to get to those wires and relays.
Can’t be all that helpful from afar since I have not seen that model tractor, but a couple of generic suggestions: Perhaps that T handle has a set screw or the like which can be accessed after the cover is pulled back part way? Or maybe it pushes in and turns to release? Just a few thoughts on how they might have attached it. Depending on how friendly the dealer is, you might want to ask the service dept there how to remove the handle/cover.
A couple of other thoughts for once you get past the cover thing: Just curious if you have checked the battery voltage. If it were low, or run down from this electrical issue that may be why the starter doesn’t come on. Also, would be a good idea to figure out which circuit(s) the melted wires run to. Either by tracing them back or looking at a wiring diagram. Even with a wiring diagram, would be good to trace the wires over their run (as best you can) to look for worn spots that may be shorting out (assuming the GPs and relay check out OK and they aren’t the source of the blown fuse).
I would not suggest replacing a fuse with a wire, even for a short period of time (even though I have done it myself on several occasions). Unless you are very sure of what the circuit powers, you run the risk of burnout some component or even a switch. That said, if/when I do try it, I typically will use a much smaller wire, one that will heat up and melt quickly like in a sec or two (sort of my own fusible link if you will), although even that has some risks. It is best to identify and fix the problem before powering it up again.
One last resource, there are a few tractor forums, tractorbynet.com is the one I use a lot. They have things organized by manufacture and model, so you can target an audience familiar with your tractor and hopefully your problem. You might look or ask there about your problem. And you might be able to get the wiring diagram there too.