As pandavova said in their post, you open the system file in HxD, then go to offset 00000338 (go to line 00000330 then column 08), then change every values from that point on to FF until the very end.
Go back to the first line (offset 00000000), go to column 0C, highlight everything from that point on until the very end of the file, go to Analysis tab > Checksum > Checksum-32 > Click OK. Check the values that it gives you, then change the first 4 bytes accordingly. For example, if the Checksum value is 0000693A, change first 4 bytes to 3A 69 00 00. In my case, the Checksum value is 000133EA so I change my first 4 bytes on the very first line to EA 33 01 00.
I'm not really good with explaining though so that's the best I could do. I believe that pandavova said they're going to write a small tool to help on that if you're willing to wait.