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.

afaik find works only on file properties but not on contents whereas sfk 'greps' through the file content

Why not?
If the path (or just the name) to the file is hard-coded then you might change it via hex editing. Take care to use same length of the string!

I have been looking into how this stuff works.
I can tell you that the list of icons you get to pick from when you create a new status (the house, factory, soccer ball, palm tree etc) is hardcoded into librtcom-presence-ui.so

As for the custom IM statuses, they are stored in /home/user/.osso/.rtcom-presence-ui.cfg and that specifies an icon name.

The icons you get on the status bar itself and in certain other places (white circle with x for offline, green circle for online, red circle with horizontal line for busy, green circle with exclamation mark for error, red circle with exclamation mark for other error) are also hardcoded into rtcom-presense-ui.

Hopefully this information helps out whoever it is that needs information on status icons

Thank you jonwil for taking the time to look into this, it would have taken me a lot more time to find it by myself.
Now I have to see how I can manage to edit the librtcom-presence-ui.so file ; if it is even possible.

BTW : what is your method to find these informations? Do you simply look for everything that seems to be related to what you are looking for and try to understand the logic behind it? How did you even know that some info is hardcoded in librtcom-presence-ui.so (I opened it with an hex editor but it looks like a foreign language to me).