Hi inked, you're imagining things as too complicated. The process is
1. remove the old strut, which you will need to do whatever rout you take.
2. The old strut is oil ... The new insert is gas. So after watching the video posted earlier get your man to .....
3. Drill a hole in the base of the OLD strut and drain the oil
4. Use an angle grinder to cut off the top of the OLD strut tube
(clean up and paint as desired)
5. Place new gas insert into OLD strut and draw into place using the screw through the base drain hole.
Job done .... put back together again.
The Konis are well designed for this job and make it really simple. For me the adjustable Konis were €300 a pair, rear Bilsteins €250 a pair, labour €180, so just over €730 all done and fitted. That compares very well with buying original Boge struts which in any case are already 10 years old.
Take the leap. If you are thinking of selling then new struts are a +ve whereas a sloppy ride is a -ve and may lose you a sale.
Good luck.