InstallationDirectory has changed from 10.3 to 10.4. If you want to keep customized items across minor releases put them in analogical places inside $UserBaseDirectory.
Instead of messing with Installation Directory you can modify/copy appriopriate files in/to UserBaseDirectory and safely edit them. Moreover, UserBaseDirectory is version independent (usually).
So the point is, keep ContextMenus.tr in UserBaseDirectory / SystemFiles / FrontEnd / TextResources / ContextMenus.tr.
For example, here is the analogical procedure of customizing MenuBar with additional items by moving and editing appriopriate files:
Danke for the link. I get your point, but my actual problem is missing the “Copy as &Bitmap”. I am curious if it works on the Mac or under Linux. I have not had much time to experiment so far.