Well, it basically will be trial and error.
All the SNES repro writing functions are in flash.ino. You can have a look at the commit for V1.6 where I added support for the S29GL032 flashrom to see what it takes to add a new flashrom: https://github.com/sanni/cartreader/commit/b816918e70a14b5fb62a4e2ec0ea298dc8b3069f?diff=unified
The Cart Reader should give you the flash ID together with the unknown flashrom error. Which you can use to create a new entry in the "void id_Flash8()" function. There you define the flashsize in bytes and whether or not it's a native 8bit flashrom (type 1) or a a 16bit flashrom in 8bit mode (type 2).
Then in the function "void flashromMenu8()" under "case 3:" you add a new entry that selects a write function based on the flash ID of the MSP29LV160. Since MSP29LV160 sounds similar to MX29LV160 I would start with the "writeFlash29LV640()" function and see if it writes anything. If it doesn't try the "void writeFlash29GL()" function.
If that also doesn't work you can have a look at the write functions of the MSP55LV128 in GBA.ino or the MSP55LV100S and MSP55LV512 in N64.ino and see what they do differently. Then with that knowledge you can create a custom "writeFlashMSP29LV160()" function in flash.ino.
Also after each time trying to write something always read out the flashrom again and check what has been written in a hex editor like HxD to see if maybe part of your write code is working.