You are brave. I have not ever tried to repair a PCB unless its an old 1970s kind with ginormous components lol.
We did solder on that sensor lead where needed, but I had my little brother do it for me.
I would not mind giving it a whirl if I have a similar problem though, particularly because I have so many spare parts from stuff breaking.
Ok, you were right, this is an easy and fast doing mod. I just soldered some Y wire and mounted the 5015 fan there. Then I printed your nice stl from thingiverse and it works without any problem. I had just cylindrical m2 screws but it looks nice, fitting is good. Just again + and - differs from snapmaker to my fan, so i have to take care to connect correct fan to correct jack on my adapter. Hopefully I do not have to change the fan often.
I will see when I will print with that head again because with new dual extruder door, the dual extruder works really great and there is normally no need to use the old head, but who knows. No I am prepared. 
I did not installed any diode.
Nice! That one looks pretty good, its different from the few I tried.
I had designed a part that looks like would go well on your module
Snapmaker 2 3DP Module Wire Entry Cover by MooseJuice1983 - Thingiverse
Its for the wire
