Got this from oeminsigniaparts.com:

The instructions he has on the website do a pretty good job, but typical GM instructions do leave much to be desired. Here is a quick run-through of the swap:

Starting with the bumper, there are 6 bolts under the hood, all T20 Torx:

3 Bolts in the fender-well, T20 Torx:

4 Plastic retainer clips under the bumper:

     

Once that is all loose, you can just pull the bumper out from under the headlight:

There are two electrical connectors that you will need to undo before fully removing the bumper:

There was one HIDDEN bolt, not listed on GM's instructions on the driver's side. It is strange because there is not a matching bracket on the passenger side You will want to do this BEFORE the electrical connectors and attempted bumper removal, LOL... I didn't know it was there:

     

Remove the foam crash bumper:

     

The only thing holding the grille in place at this point is 27 little plastic tabs:

These seem easy enough, but it is a combination of unlatching these and BRUTE force to get the damn grille loose. It had my buddy and I scratching our head trying to figure out how to get this off until we finally just gorilla'd it off. Sorry, no pics of this part cause we were too frustrated.

After that, the new grille just snaps into place on the clips, and viola:

     

Next was the engine cover badge, just take the hose off that runs along the front of the cover:

...and you can then lift the cover straight up. The buick badge is held in place with little plastic retainers, just bend these all straight and the badge will come right off:

The Opel badge just clips back in its place:

The wheel center caps are pretty straight-forward, just pop off, pop on:

I was worried about the door sills, because the instructions seem "complicated" on the website, but upon further inspection.... they are just metalized stickers and pull right off:

Followed by replacement with the Opel. I used some masking tape to mark the location of the stockers:

Finally, the trunk. I had already debadged the Buick and Regal GS logos so no pics of that. But, that is just a simple matter of a heat gun or hair dryer to loosen them... then some adhesive remover to get the gunk off that is left.

The Buick badge itself is just held in with pressure clips... so just pry on that and it pops right off:

HOWEVER, there was a surprise... and my first one of the day. Behind the Buick badge is black plastic. I knew from my prying before I started that this piece was seperate from the actual Buick badge, and I assumed that it would be reused with the Opel... I thought wrong:

The black plastic is SPECIFIC to the Buick, and the kit did not come with the Opel counterpart for this piece. In fact, the Buick plastic is curved versus the Opel being flat so there was no way for it to be reused. If you look at the Buick parts diagram, it does have a separate part for the black plastic, #8 below:

However, on the Opel parts diagram, there is no matching piece:

I am still trying to track down the necessary part, but I decided to fashion my own plastic from a CD case as suggested by a forum member. It took about 3 different attempts to get it perfect:

In the end, it came out very nice:

Lastly, the rear badges... I used masking tape to get the location and level perfect before removing the adhesive backing:

          

Next moving to the interior to complete the transformation. I know many of you may be scared about the airbag portion, but I have done close to a dozen airbag swaps and they are incredibly easy with very little tools/time required!

Step 1. Disconnect the negative terminal on the battery.

Honestly, I have done airbag swaps without disconnecting the battery but it never hurts.

Step 2. Spring Clip Removal

For almost any car I have worked on, there are usually small access holes in the steering wheel to access the spring clips that hold the airbag in place. For most late model GM vehicles, that is usually on the side of the steering wheel. Leave it to the Germans to make it a little more difficult to find, it took me a while to figure out where they hid the access holes and had to consult the service manual.

For the Regal, it is actually on the back of the steering wheel. Usually you can just use a straight, thin screwdriver to pop them loose, but the Regal's unusual location requires a "special" tool.

Here is what the service manual shows:

You may be asking where you buy such a tool... well, there isn't one. In the service manual it tells you to fashion your own from an old screw driver LOL. It says to make a 30* bend around 1" from the tip. I decided to make my own from an old allen wrench:

Now that you have your tool, you may be asking "how does this possibly release the airbag?" Very simple... turn your steering wheel 90* right or left from center and if you look behind the wheel you will see the access hole. You simply insert your tool till you feel the spring clip, press down (lift up on tool) and you will feel the spring clip release and that side of the airbag will be loose:

Then simply rotate the airbag 180* the other direction to access the other access hole and repeat. This picture from the service manual should help:

Step 3. Wiring

Once the airbag is loose, flip it over and there are two wires connected to it:

To remove these wires, simply lift up the plastic retainer on the top of the connector, this retainer is NOT removed, it just lifts up:

Once that is loose, the connector simply pulls straight off from the airbag:

Step 4. Airbag removal.

Viola... your airbag is now removed:

Step 5. Reinstall

Now to reinstall you simply reconnect the cables on the new airbag, they are color coded so you can't mess it up! Just push them straight on to the new airbag, and press the plastic retainer back down to lock it in place.

The new airbag is reinstalled by just lining it up in the correct location and pressing firmly until it locks in place.

Step 6. Reconnect Negative on Battery

A few small details when you disconnect the battery:

1. The clock will lose its time, but will pull the updated time within a few minutes from XM if you have a subscription
2. The windows will need to be "reset" by lowering and raising the front two windows
3. The compass will need to be recalibrated, but should happen automatically once you start driving

That's it! Now that I know where the darn holes are in the steering wheel, I could do this swap in all of 10 minutes! ...it is incredibly easy and I hope this write-up helps you tackle this swap.

I also removed the "GS" from the passenger side only to find two small holes in the piano trim for badge alignment There doesn't appear to be an Opel counterpart for this badge so I found an easy solution, the Piano black trim from the non-GS is only ~$60 on GMPD, part #13274857 so that should be an easy fix to get rid of the holes on that side.

The trim is only held on with clips, so simplying prying on it will release it from the dash:

          

Now just reinstall the new piece and tada... no more holes!

Overall I am very happy with the conversion, it went very smooth and even taking our time it was a 2-hour job max.