I already did a search on the device with the command find with the words "presence" and "test" (test being my custom IM status), but with no relevant result ; so I decided to post on the forum, but I will also try with your console tool (sfk).
Sadly if the value is in a library I wouldn't have the possibility to change that (or did I misunderstood that?).

But I find it weird that a custom IM status whose title and presence preferences were define to be what I wanted doesn't have a text file with some infos in it.