^^ What they said ^^
I have shortened Hope's 6 months ago and they had to be bled after. I shortened my Magura's 2 weeks ago and didn't have to bleed them. Also, I shortened and bled my hydraulic lockout and what Jim is saying about the barb and olive is key. I made sure I had a bleed kit, barbs and olives, but I was also able to slice open the cut cable and remove the barb. The olive, however, is delicate and if you compress it at all it will be super hard to save and get back onto the new hose.
Anyway, if you have the kit and parts, any bleed is pretty simple nowadays. Plus there are videos for everything.