Herewith my images how I shortened the 60 cm bar to 49 cm:

the 60 cm bar before “molesting”

cutting the first bar end

drilling out the remains of the bar from the bar end.

both bar ends cleaned out.

bar cut to size and eva foam removed to fit both bar ends

glued the foam back in the hollow bar to make sure the glue for the bar end is not squeezed into the hollow bar

The glue I have used is methyl acrylate. Many thanks to Rudo!
I understood that this glue bonds better with the hardplastic end caps than epoxy…

use enough glue for proper bonding - so much that you squeeze some out.

tadaa, bar shortened to 49 cm. The bonding of the bar ends to the bar is tested by hanging on one of the ends with my weight, with hooking the other side to the topside of a door.
A bit scary to start this project but it’s pretty easy to do. It’s alway’s good to know your gear.
Thanks Rudo and Jtrashy for your advice!