whoslooking: I did some fast hexrays decomplation and there is region code also in hardware description block. I change it to something else than CH and I was able to upgrade cameras to the newest 5.4.0 software.
Here is part of serial creation function from 5.2.3 davinci binary:
switch ( *(_BYTE *)(v4 + 85) )
{
case 1:
case 0x20:
v25 = strlen(v3);
memcpy(&v3[v25], "CH", 3u);
break;
case 2:
case 0x32:
v26 = strlen(v3);
memcpy(&v3[v26], "TW", 3u);
break;
case 3:
case 0x30:
v27 = strlen(v3);
memcpy(&v3[v27], "WR", 3u);
break;
case 4:
case 0x31:
v16 = strlen(v3);
memcpy(&v3[v16], "HK", 3u);
break;
default:
v24 = strlen(v3);
memcpy(&v3[v24], "RR", 3u);
break;
case 0x21:
v17 = strlen(v3);
memcpy(&v3[v17], "BJ", 3u);
break;
case 0x22:
v18 = strlen(v3);
memcpy(&v3[v18], "SH", 3u);
break;
case 0x23:
v19 = strlen(v3);
memcpy(&v3[v19], "GZ", 3u);
break;
case 0x24:
v20 = strlen(v3);
memcpy(&v3[v20], "CD", 3u);
break;
case 0x33:
v21 = strlen(v3);
memcpy(&v3[v21], "JP", 3u);
break;
case 0x34:
v22 = strlen(v3);
memcpy(&v3[v22], "AS", 3u);
break;
case 0x35:
v23 = strlen(v3);
memcpy(&v3[v23], "EU", 3u);
break;
case 0x36:
v14 = strlen(v3);
memcpy(&v3[v14], "NA", 3u);
break;
}