I'm surprised that there isn't a tutorial (or I haven't found one) that details converting to negative earth. I've done it myself, but I'm very electrically capable, so depending on your electrical skill set it might be more difficult for you. However, basically these are the things that need to change:
1) Your charging system. With aftermarket rectifier/regulator that's just a matter of swapping 2 wires. With the stock bridge rectifier / zener diode setup it means swapping the +/- terminals on the rectifier and installing a new zener diode that is polarized for negative earth. Fortunately negative ground is the "standard" zener polarity (case is negative) and the zeners are available from electronics suppliers like Mouser and DigiKey. The part number would be 1N3313B which is a 14 volt 5% 50 watt stud rectifier. You'd have to solder a 16 ga. wire with a 1/4" male spade to the cathode terminal, and the nut will be 1/4-28 NF instead of the 1/4-26 cycle thread on the Lucas zener.
https://www.newark.com/solid-state/1n3313b/zener-diode-50w-14v-do-5/dp/56J9299?ost=1n3313b
2) Your electronic ignition. You said in a PM that you have a Pazon. That and the ignition coils need to be rewired. I'm sure the installation instructions would cover that.
3) The battery. The +/- need to be swapped. That's the last step.
The only downside to this procedure is that you have to remember that all the red wires in your harness are now NEGATIVE.
I did it on my own bike some 10 years ago to take advantage of standard automotive LED's in the blinkers and tail light. That was before non-polarized LED's were available. No regrets.