No big work unless the key gets stuck. Replacing the tumbler is routine. Just takes being able to turn the key to position 1 and a bit of jiggling and luck to get the tool in the right position. The pain would start if the key gets stuck or you get the key in there and you can't turn it to position 1, then you are talking about drilling the thing out.

glenmore
1991 300CE
2000 C280

(Corrected post. Key position to remove tumbler is #1)