It looks like the only difference between the two is the "shoulders" at the end; can I just shave-down the sides of the valet key-end to have the same shoulders and it will work like the regular key?

Is there any difference in the electronic-transponder for the valet key?

Basically, I have no use for valet mode and need an additional key that will let me open the trunk/fuel-door.

 

No difference in the guts. It is only the tip that is different.

 

There was a thread on this but I can't find it.
Here are the two keys

To mod your valet key carefully file the tip to 4.5 mm (0.175") diameter for a depth of 2 mm (0.08").
Take the same amount off both sides of the key.
My two master keys measure 4.5 and 4.4 mm at the tip so a bit under 4.5 mm is OK

 

Awesome! Thank you for the prompt detailed response.

Has anyone actually done this and can confirm that it does not ruin the key in some way? (concerned that the key would be non-valet but transponder tells car it is valet or something like that)

 

Yes, do it. The transponder, as Plums said, is the same on both keys.
It has been done several times and, provided you take your time with the file, it will work.

 

You won't even have to reprogam it as the SLM does not know the difference.

 

thanks for the tip - literally. I had only 2 keys, one black and one green key. I followed your info and shaved down the tip to ~4.5 mm. I used my original black key as a guide. Now I have two master keys! Thanks



tip shaved on valet key to make additional master key

 

And here’s me lamenting about not having a Valet key and wanting to complete the set 😂

 

This post is from a decade ago, but confirming that I had a locksmith do it and it worked prefectly. The locksmith didn't even charge me, he said he himself was curious if it'd work - took him maybe 1 minute.

 

Nice locksmith...I would keep his number around.