I found this how to very useful.
I did it today.
I removed the 1 o'clock, 4 o'clock 8 o'clock and 11 o'clock allen fitments. Don't wiggle them out. I just turned them out slowly keeping pressure on with an allen key. The rotating action does not break the retaining clip underneath. My test fuel cap had a couple broken clips when I wiggled. They were rusty. I cleaned everything. Brake cleaner got rid of 17 years worth of grime. I took the test cap to pieces. It did have 6 plastic lugs holding everything in place. 3 of the lugs are on a plastic ring which can be removed when you take the blue inner part off. I did not want to do that to my good cap that I was adding the chrome surround to. There is a knack to removing the luggs though. The larger luggs that are the same on the mk1 cap are easy to move. The solid luggs on the ring are not as easy. I did not try to push everything out in one gobut eased out the top larger lugg. Then moved around to the solid one next to it. I managed to pivot the inner cap inside the surrounf and the plastic ring had a bit of movement then. I moved on to the next lugg and after doing three the others just became easier to work out.
I would not have known this if I had not taken the sacrificial cap to pieces. Parts of it did break. This was due to the cold. The luggs are a little brittle when cold. I used a hair dryer to warm everything up a little.
Putting the new surround was a process of working around the luggs one at a time. It helped to spray a little 3in1 toease the luggs back in to place. The last solid lugg was not wanting to engage. I used a small hook tool underneath it to clip it in to place. I was going to use a soldering iron to melt a bit of the lugg over the chrome ledge it had to sit on. No need in the end.
If your luggs do break the inner black lock part will not hold very well. This can be fixed by drilling a small hole and pushing a rod into the hole to overlap the ledge on the surround.
Cleaning the allen fitments. Use an allen key to hold the fitment and twisle it around some Duraglit.
If I can do this anyone can. Happy dayz.