editing system file android 4.2.2

[revd@wallaces.org]

I must be missing something.
I wish to add a permission to /system/etc/permissions/platform.XML
(Adding <group gid="media_row" /> to write external storage allows apps to read write externalsdcard allowing backup programmes to work with external card.)

Using total commander setting / and /system and /system/etc/permissions/platform.XML to being remounted rw all seems to be set allow edit of platform.XML.
However when it comes to saving the edited file total commander gives error message then message to remount rw . Even on so doing error message again comes up on trying to save and again message to remount.
What am i missing?
How do I achieve my intent?
Was no problem on android 4.1 !
Must be glitch in T.C ?

Yes. Device is rooted and has current busy box pro and superuser.
Best wishes
David

[ghisler(Author)]

What permissions does the file itself have (Long tap - Properties)?

[revd@wallaces.org]

Went back and double checked permissions/platform.XML have rwx as does /, /system, and /system/etc

Best wishes
David

[revd@wallaces.org]

Also updated TC to latest beta version
Best wishes

[revd@wallaces.org]

Any solutions from TC author or other experts?
I'm coming to the view changes have been made Android 4.2.2 from 4.1 limiting access to file system.
Best wishes
David