For the moment is not possible. I'm trying to understand how this save file works but its too hard to understand (almost for me). The save file has (minimum) 2 files: userX and system.
The userX is the user X data like money, items, weapons, etc, where X is the slot number of your character. The file is encrypted of course... I found a webpage that can modify your hunter's name and palico's name. I tested it and I saw that at the offset 0x0000 - 0x0007 it has some type of cheksum that changes always you modify your name.
http://my1993.com/wip/mh4genc.php
Also I found Palico's offset name 0xC4B8-0xC4BF and Hunter's name offset 0x0038 - 0x003F. But also, some other bytes are implied... This log shows the diferences after chaning Hunter's name and Palico's name.
SAV user1 - 1 Pos[0x00] = 0x56
SAV user1 - 1_edit3 Pos[0x00] = 0xEB
SAV user1 - 1 Pos[0x01] = 0xDC
SAV user1 - 1_edit3 Pos[0x01] = 0x76
SAV user1 - 1 Pos[0x02] = 0x1E
SAV user1 - 1_edit3 Pos[0x02] = 0xEF
SAV user1 - 1 Pos[0x03] = 0xD0
SAV user1 - 1_edit3 Pos[0x03] = 0x3B
SAV user1 - 1 Pos[0x04] = 0x50
SAV user1 - 1_edit3 Pos[0x04] = 0x2E
SAV user1 - 1 Pos[0x05] = 0x2D
SAV user1 - 1_edit3 Pos[0x05] = 0x0B
SAV user1 - 1 Pos[0x06] = 0x3B
SAV user1 - 1_edit3 Pos[0x06] = 0xD3
SAV user1 - 1 Pos[0x07] = 0x46
SAV user1 - 1_edit3 Pos[0x07] = 0xD8
-----------------------------------------------
Bytes: 8 |Offset: 0x00 - 0x07
-----------------------------------------------
SAV user1 - 1 Pos[0x38] = 0x97
SAV user1 - 1_edit3 Pos[0x38] = 0xEA
SAV user1 - 1 Pos[0x39] = 0x6D
SAV user1 - 1_edit3 Pos[0x39] = 0x14
SAV user1 - 1 Pos[0x3A] = 0xB7
SAV user1 - 1_edit3 Pos[0x3A] = 0xC2
SAV user1 - 1 Pos[0x3B] = 0x88
SAV user1 - 1_edit3 Pos[0x3B] = 0xDD
SAV user1 - 1 Pos[0x3C] = 0x67
SAV user1 - 1_edit3 Pos[0x3C] = 0x42
SAV user1 - 1 Pos[0x3D] = 0x50
SAV user1 - 1_edit3 Pos[0x3D] = 0x82
SAV user1 - 1 Pos[0x3E] = 0x19
SAV user1 - 1_edit3 Pos[0x3E] = 0xD1
SAV user1 - 1 Pos[0x3F] = 0x1E
SAV user1 - 1_edit3 Pos[0x3F] = 0xD8
-----------------------------------------------
Bytes: 8 |Offset: 0x38 - 0x3F
-----------------------------------------------
SAV user1 - 1 Pos[0xC4B8] = 0xAF
SAV user1 - 1_edit3 Pos[0xC4B8] = 0x85
SAV user1 - 1 Pos[0xC4B9] = 0xCC
SAV user1 - 1_edit3 Pos[0xC4B9] = 0x44
SAV user1 - 1 Pos[0xC4BA] = 0x2D
SAV user1 - 1_edit3 Pos[0xC4BA] = 0x23
SAV user1 - 1 Pos[0xC4BB] = 0x19
SAV user1 - 1_edit3 Pos[0xC4BB] = 0xD6
SAV user1 - 1 Pos[0xC4BC] = 0x07
SAV user1 - 1_edit3 Pos[0xC4BC] = 0x48
SAV user1 - 1 Pos[0xC4BD] = 0x3B
SAV user1 - 1_edit3 Pos[0xC4BD] = 0x2B
SAV user1 - 1 Pos[0xC4BE] = 0xF7
SAV user1 - 1_edit3 Pos[0xC4BE] = 0x08
SAV user1 - 1 Pos[0xC4BF] = 0xB3
SAV user1 - 1_edit3 Pos[0xC4BF] = 0x4F
SAV user1 - 1 Pos[0xC4C0] = 0xA5
SAV user1 - 1_edit3 Pos[0xC4C0] = 0xBD
SAV user1 - 1 Pos[0xC4C1] = 0x54
SAV user1 - 1_edit3 Pos[0xC4C1] = 0x84
SAV user1 - 1 Pos[0xC4C2] = 0x0D
SAV user1 - 1_edit3 Pos[0xC4C2] = 0xF4
SAV user1 - 1 Pos[0xC4C3] = 0x9C
SAV user1 - 1_edit3 Pos[0xC4C3] = 0xD4
SAV user1 - 1 Pos[0xC4C4] = 0x12
SAV user1 - 1_edit3 Pos[0xC4C4] = 0x5F
SAV user1 - 1 Pos[0xC4C5] = 0x37
SAV user1 - 1_edit3 Pos[0xC4C5] = 0x8A
SAV user1 - 1 Pos[0xC4C6] = 0x9F
SAV user1 - 1_edit3 Pos[0xC4C6] = 0x4C
SAV user1 - 1 Pos[0xC4C7] = 0xB6
SAV user1 - 1_edit3 Pos[0xC4C7] = 0x98
-----------------------------------------------
Bytes: 16 |Offset: 0xC4B8 - 0xC4C7
-----------------------------------------------
Bytes readed: 81408
Diferent bytes: 32
I would apreciate if someone want and can help me to create and mh4 sav editor
Thanks in advance.