At leats with the packages on people.debian.org it does not work. The 10texlive-base.cnfpre-edit files is still there and the lines did not make it into 10texlive-base.cnf. I added some dummy lines to check if sed is simply intelligent enough not to add duplicate lines, but this is not the case.
Ouch, hmm, can you recap me how to reproduce the problem? I remember we need some special conf file ... and then update. I will retry myself and try to fix it. Norbert