I am not aware of CMSSW-wide restrictions for `friend`, but the current approach is forbidden:
http://cmsdoc.cern.ch/cms/cpt/Software/html/General/CodingAndStyleRules.pdf
--> 4.2
It is the first item on your to-do-list from last week anyway, and I consider it a "conditio sine qua non".
Please fix this.
I am ok with adding corresponding `friend` access functions to the PAT objects, but of course I cannot speak for the POGs.