Top & Tailing Laser 1 mast sections

I have been advised to Top & Tail my mast sections and am looking for advice. My Laser is a 2004 Australian one.
1/ is it ok to reuse the old plugs and collars or are there advantages in using new.
2/ when inverting sections do I leave in same plane so the back of the mast is still the back, or rotate 180 degrees so what was back is now front, or do I rotate 90 degrees so front & back are now at the sides.
3/ Do I need to plug the old rivet holes and if so do I use rivets, silicone, epoxy, anything else.
I will most likely use Monel rivets or should I use Stainless Steel or Aluminium.

1) No point in getting new fittings unless you end up damaging (or downright destroying) the old ones in the process. I changed my front boom plug a couple of years ago, and I didn't get the old one out until I sawed it in half. (Now I know why the reinforcement sleeve kits include a new plug.)
2) Probably makes no difference.
3) You must plug all the holes in the upper mast so that it stays watertight. Aluminium rivets and/or silicone.
If you're thinking about rivet material in general, I guess stainless makes sense for everything load-bearing, and aluminium for everything else. Monel could of course be a good compromise.

I've just spent a whole evening drilling stainless rivets out of Topper lower mast sections. The corrosion has forced me to scrap 2. This is because SS is noble and aluminium is reactive. So if you have to use stainless as monel is expensive, bed your fitting down on some cheap silicone to act as an insulator, especially if you sail in salt water. Use aluminium rivets for filling holes. I've spent more time on the club dinghy fleet correcting electrolysis problems than any other fault.
All our laser lower mast sections have bad corrosion under the vang attachment. They will all have to come off this winter

Follow up question.
I successfully inverted the top section.
I was also advised to invert the bottom section (Radial & Standard) because there is some corrosion setting in around the vang & gooseneck. This does not look too serious yet but more preventative maintenance.
After taking bottom plug off radial section I noticed an inner sleeve, which after looking At laser rules I see this is standard.
Before I start drilling out rivets can anyone advise me if this sleeve is just held in with the rivets and will I be able to move it once they are drilled out or am I asking for trouble even attempting it.
I believe I should not have same problem on the standard mast.