Yeah thats right. If you buy the ones from eBay in the link, then they come as loose self adhesive letters, you can then just heat yours up to help removal, remove just the letters and then stick the new ones on.
You will see that the new ones are slightly larger and the red cube is larger than the backing plate, but I think it looks fine....
I have actually just seen that there is someone selling a very similar to OEM badge on eBay now, which wasn't around before but I think this will mean you will have to remove your OEM entire badge which I think is difficult and may be a grill off job...
So here are the ones that I bought (and then coated with clear gloss top coat):
https://www.ebay.co.uk/itm/Black-RS6-Gr ... 2749.l2649
And here is the new badge, BUT my guess would be that this comes as a complete badge and not with the characters separate...
https://www.ebay.co.uk/itm/Audi-RS6-Glo ... SwYUpdtf5A
Take your pick!
Cheers,
Lig.