I made a Lv.1 mod a while back, which should be in the 7H Catalog. I think I handled Cait and Vincent by going into the kernel and setting their Join Level modifier to 0 (should be on the exp arc screen). Their initial starting stats, however, weren't modified. as these are stored in the .exe and then used to overwrite the kernel (which initially holds Sephiroth + Y.Cloud).
I think best route would be to grab the Lv.1 mod from the Catalog, unpack it, then take the scene + kernel out of it then make adjustments to the kernel for desired initial stats + curves. After that, try to locate the hex address of Cait and Vincent's starting stats and change them to what you want them to be.
These are the notes I have on the addresses but I should mention that I can't remember if they were correct or if I ever tried changing them, etc. They might not even be for PC, just had them floating around in a notepad along with a bunch of other bits and pieces:
Cait Sith's Level : 0x520c11 (120011) (1 byte)
Cait Sith's CurrentHP : 0x520c3c (12003C) (2 bytes)
Cait Sith's Base HP : 0x520c3e (12003E) (2 bytes)
Cait Sith's Current MP : 0x520c40 (120040) (2 bytes)
Cait Sith's Base MP : 0x520c42 (120042) (2 bytes)
Cait Sith's stats* : 0x520c12 (120012) (1 byte each)
Cait Sith's weapon : 0x520c2c (12002C) (1 byte)
Cait Sith's armor : 0x520c2d (12002D) (1 byte)
Cait Sith's accessory : 0x520c2e (12002E) (1 byte)
Materia on his weapon : 0x520c50 (120050) (4 bytes for each materia slot -
first byte is the materia ID, and
the next 3 bytes are its AP)
Materia on his armor : 0x520c70 (120070)
Vincent's Level : 0x520c95 (120095) (1 byte)
Vincent's CurrentHP : 0x520cc0 (1200C0) (2 bytes)
Vincent's Base HP : 0x520cc2 (1200C2) (2 bytes)
Vincent's Current MP : 0x520cc4 (1200C4) (2 bytes)
Vincent's Base MP : 0x520cc6 1200C6) (2 bytes)
Vincent's stats* : 0x520c96 (120096) (1 byte each)
Vincent's weapon : 0x520cb0 (1200B0) (1 byte)
Vincent's armor : 0x520cb1 (1200B1) (1 byte)
Vincent's accessory : 0x520cb2 (1200B2) (1 byte)
Materia on his weapon : 0x520cd4 (1200D4) (4 bytes for each materia slot -
first byte is the materia ID, and
the next 3 bytes are its AP)
Materia on his armor : 0x520cf4 (120000)
* Stats are listed in this order : strength, vitality, magic, spirit, dexterity, luck.