Blimey.
I just did the same; changed to braided cable and it refused to bleed well with my handy "brake bleeding kit".
I left it overnight with the lever tied back to the grip (you can do the same with cars by chocking the brake pedal down) which is my usual patent safe method. That didn't work but I had a wedding Saturday.
I came back to it on day three (Sunday) and the "lever tied back" method still hadn't worked BUT it then bled correctly at that point.
Dunno.
I assume lots of air in the system that just needed to work their way out.
Lever is not actually any firmer than before BUT I cannot now feel the upper hose expanding.
Road test next (with the new rings, camchain etc) - will it go and stop better ....