I have been trying.
no way it does not work.
Under windows the file seems to be in c:\users\yourusername\exiv2.ini
Lensfun database identifies this lens as follows
<maker>Tamron</maker>
<model>Tamron SP 70-200mm f/2.8 Di VC USD A009</model>
<model lang="en">Tamron SP 70-200mm f/2.8 Di VC USD</model>
I was not sure if A009 is needed or not.
As I have reported earlier, using exiv2 to get lenstype and model gives you
0x0016 CanonCs LensType Short 1 255
0x0095 Canon LensModel Ascii 74 TAMRON SP 70-200mm F/2.8 Di VC USD A009
0xa434 Photo LensModel Ascii 40 TAMRON SP 70-200mm F/2.8 Di VC USD A009
So I have tried every combination of them
[canon]
255=Tamron SP 70-200mm f/2.8 Di VC USD
[canon]
255=Tamron SP 70-200mm f/2.8 Di VC USD A009
[canon]
255=TAMRON SP 70-200mm f/2.8 Di VC USD A009
with no success under darktable.
I have closed and opened darkatable each time with no success.
The difference is that when i run now exiv2 it reports LensType for the provided name and not as 255
Exif.CanonCs.LensType Short 1 Tamron SP 70-200mm f/2.8 Di VC USD
So it seems that exiv2 is reading the exiv2.ini file and working, but not darktable.
May be it only works in the command line tool and not the library.
But darktable reports lens as 255 each time.
I can provide a raw file if demanded in order to see if it just a problem with windows or it happens in Linus too.