As stated above, you can try the editor I wrote:
github/Tonic-Box/D3Studio
As for the error, it means that its having issues reading your save, meaning either:
A) the python editor here has a wrong protobuf definition for some field somewhere (Probably a field listed as wrong type etc)
or
B) if...
Was looking at the sources of traffic to my github and noticed GBATemp on this list. Really appreciate the shout-out guys <3
Genuinely appreciate it :) Think I'll make a thread of it's own on here shortly once I break out of the newcomer restrictions.
Also it workd for switch, ps3/ps4, and...