pax, just wondering, by changing that icon, what do you expect to change ?
Linux uses the icon in, eg /usr/share/icons/hicolor/256x256/apps/$APPNAME.png and some times the one pointed to by your desktop file.
I think something uses the embedded but unsure what it is. Generally, the above applies.
(And, I note your new install of Lazarus rc3 now has yesterday's build date - what on earth is happening there ?)
Davo