I used the tips from Sheldon Brown and from this website.
However, when I tried to pull the new, splitted, inner tube through the tubular by attaching it, with a knot, to the old inner tube the old one snapped.
So I had no inner tube left in the tubular.
As a result I had to, do not know the wright English term, "feed" a string line through the tubular which went quite easily.
I used the string line, attached to the new inner tube, to pull the new inner tube through the tubular.
Next time I will not try to pull a new inner tube directly with the old one through the tubular. The knot is to big and most likely it will snap. Pull a string line (small but strong line) through the tubular with the old inner tube and use the string to pull the new inner tube. This will work much easier. Use talcum power. This will fascillitate the "pulling through".
For joining the end of the new innertube I used the same manner as described in the part "Splicing the Tube". I only used 3 cm's instead of one for rejoining and I was carefull not to get any glue past the joining parts. I used normal patch cement which worked ok. I tested the seam with a little, pressure.
I re-stitched the tubular with waxed dental floss and I tried to use the existing holes as much as possible. Be carefull not to stitch into the floss again when going backwards because it will tear. After checking air tightness at 9 barg a glued the base tap back with Bison Kit. (a flexible contact cement and I think allmost the same as Barge Cement)
The tubular is on a spare rim and I kept it inflated at 9 barg for several days and it was holding fine.