Here's my noob step by step modifyin a game mesh so far :
Make a backup of your game folder To easily identify mesh u want to modify : i use UnityStudio x64 v0.9.0/ load game "data" folder (since it has a 3d model preview panel its quite useful) find mesh in asset list tab (not scene hierarchy) /right click on your mesh > show original file > that will give you the game .assets file containing the mesh You can "export selected asset" to get the .obj file of this mesh , or do it with UABE like in next step.
If you allready know what mesh you r lf:
open game file level*.assets or shared*.assets file with UABE / find your mesh / plugin>export mesh as obj modify .obj result with blender / export result as .obj run unity / in "Assets" tab >Import New Asset... > select that modified .obj (or simply drag your modified .obj on unity) It should appear now in unity "Assets" panel at bottom of ur screen > drag it up in scene (top screen ,blue sky window) & reset its position x, y, z to 0 (in right screen panel) "File" tab > build settings > build & create a result folder for it open UABE > open sharedassets0.assets file in the unity data result folder find modified mesh /export raw (it will be the 3rd or 4th one with name "defaut" prolly / anyway it will be the only mesh in top of the list / raw will be exported as .dat file) open back game .asset file with UABE , find your target mesh to swap/ import that .dat file raw result on it . click the ok button down , UABE will ask for save > save in an empty folder > then u can paste/replace the original with this *.assets file in your game "data" folder run the game ; mesh should be swapped
* Works also with any 3d model (doesn't need to export/modify that game target mesh before / any 3model raw result you built in unity can be directly imported on your target). Better load both game mesh obj & the one u r gonna replace with it in blender before unity building step ;to make sure of scale/orientation match
** I find Unity studio more pleasant for sorting /preview honestly but u can get rid of it : export all target .assets file mesh to .obj in a folder with UABE, and drag all that .obj in unity who also gives a good overall 3d preview.
*** U can also use open3dmod , who gives 3d model preview aswell.
Btw i still can't figure it out : so far i can replace a game mesh, but how can i do it with material or link it to an existing game texture 2D tyvmmmm for the noob tuto answer =P (can it be done with uabe / do i have to deal with Assembly-C-Sharp.dll & dnspy ? is it possible at all ... huhu)
Have a nice day Folks
nb last for pros : feel free to flame & correct this aswell (after you'v done my tuto i mean =P)