In Opera 12, you just enter about:config in the address bar. Then you scroll down until you find "User prefs" and expand it. The value you're looking for is "Hot list file V2" which is the location of where your bookmarks.adr file is located.
I think there is also a way to do it in the operaprefs.ini file, but I don't recall how.
Not sure about Chromra. Probably not possible, as Chrome is designed to be a "Download and go" browser. It's not very customizable.