Unity3D Editing mecanim characters through 3ds max and then importing back,causes PROBLEMS!

Hello smart people! Gonna make this quick so you can understand.
1. So I have made Mecanim character in Unity (all works perfect).
2. I want to edit/update my character model through 3ds max and then export it from 3ds max back into unity3d again (You know so that i can replace my old character with the new one i made/upgraded in 3ds max )
3. So i have edited my character model and have exported (replaced) back in unity3d.
4. So now mecanim character should have new mesh and everything i had edited in 3ds max........

But the mesh and structure of my character has completely changed,its F messed up (deformed sizes,mesh looks different and when placing character in scene it somehow dissapears,basically its all F UP!)

So i want to know,is there another way to edit MECANIM character mesh (maybe detach some parts from mesh,if needed) in Modelling studio (3ds max..) and then Successfully import model back in UNITY3D engine without any PROBLEMS.

You smart people are my only hope.
Please if you can,help me out,i will appreciate any help. Thanks!

 

Can someone HELP ME!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

Many people consciously don't answer in double posts...

 

If you did change the rig, it would be better to open up the asset in unity and reconfigure your avatar T-Stance. We cannot detect such case because we don't know what has changed in the file.

So the rule of thumb is to reconfigure your avatar if you do change your rig in your 3d tools.

 

Are you just trying to update the mesh and not the rig/skin?
You can't just re-import a mesh onto a mecanim setup character, it has to be set up properly like you did before on the old character model. If your not attempting this please excuse the confusion, but the OP sounds like the entire process to set up a character in mecanim isn't being followed.
I think the best approach is to start over from Max export into Unity and set up the character again just like you did with the first one. And follow mecanim.dev's advice.