Question How to customize existing importers ?

Hi all

I got meshes coming from blender. They have 4 UV layers: UV0 to UV3

UV2 and 3 are internal UVs that i don't care in unity.

Therefore i'd like to add features to the basic U3D mesh importer that would allow me to remap mesh UVs like this:

blender unity
UV0 --------------> UV1
UV1 --------------> UV0
UV2 --------------> none
UV3 --------------> none

Could please anyone tell me what i should start with ?

I think about some OnPostProcess in wich i would use ShowStandartInspector...
In this way can i add at the following of the standard inspector my UV swapping entries ?

Should i preferably rewrite the whole mesh importer ? ( please tell me not )

If anyone have some short example in wich there's an added parameter to std mesh importer, this would be great

Thanks in advance for your kind help !

Happy unitying !