I have a new Remington 870 Express that came with magazine tube dimples (little rectangular stakes that holds the spring retainer) and the new lockable safety.
The dimples drill out easily. It'll take about 20 minutes of work if you know what to do. Unscrew the magazine cap, take our your barrel, take out your pump and bolt, take out your spring retainer, spring, and follower. Put a layer of tape on your tube where it will touch your drill press table, or put a piece of wood between your gun and the table (to avoid scratching your finish up). You can use a 7/32 bit and drill into the dimple, flip over and do the other dimple. You won't need any fancy bit to do it, a normal split point high speed steel bit should work fine. Use a small 6" long chainsaw file (about 5/32" diameter) and get in the holes and clean it up, and then polish the inside of the tube with 120 or 220-grit sanding mandrel so the burr from drilling/filing doesn't jam your follower. Try to drop your follower down the tube without aligning the notches to the stakes and if it falls though, you did a good job. If not, file and sand a little bit more. Use a very light touch when polishing the inside of the tube, you don't want to thin the tube significantly.
As for the keyed safety, I really don't think its a problem. You'd have to try pretty hard to get it to lock without the key. You can do it if you grab it with a finger on each side and purposely try to twist, but its not something thats going to happen on accident. Its probably about as likely as having your magazine cap unscrew and your barrel fall off.