and...
YEAH BABY!!!

got it replaced automatically... even before the video is loaded ^^ *hrhr*

instructions:

1. download the zip-file and place file "rvid" in ~/MyDocs/ranvid/ (for example)
2. open xterm
3. type "sudo gainroot"
4. type "cp MyDocs/ranvid/rvid /etc/event.d/"
5. type "chmod 777 /etc/event.d/rvid"

if you haven't done it yet:
8. type "mkdir /etc/hildon-welcome.d/dconfs"
9. place your default.conf files there BUT rename them in 1.conf, 2.conf, 3.conf and so on.

so the contents should be:
/etc/hildon-welcome.d/default.conf
and
/etc/hildon-welcome.d/dconfs/1.conf
/etc/hildon-welcome.d/dconfs/2.conf
/etc/hildon-welcome.d/dconfs/3.conf
... and so on.

ehm yeah... have fun

edit: forgot to mention... this one is the code which will always replace the current bootvideo with any other bootvideo out of the x.conf files (:

EDIT: UPDATED TO FINAL VERSION. ^^