Klaus, I think you're missing the point of Free Software. First, the vast majority of the code involved in SME was not written by Mitel/e-smith; they just took existing packages and made them work well together and configure easily. I'm not trying to trivialize their work; it was (and continues to be) a major undertaking, and one which they've done very well.
AFAIK, all the e-smith-specific stuff in the unsupported developer release has been released under the GPL, which means that anybody can distribute it, for free or for a price, so long as they also distribute it under the GPL (which means, among other things, they must make the source available, and they can't stop their customers from redistributing it).
However, Mitel presumably owns the name--if you make changes (or don't) and then start selling copies, you probably can't call it the "Mitel Networks SME Server". You'd need to come up with your own name.
In short, it should be perfectly legal for somebody to distribute modified copies of the unsupported release, so long as he didn't try to pass it off as Mitel's product, and so long as he complies with the GPL. Of course, if anybody from Mitel were to express a contrary opinion, I'd be inclined to pay attention. Of course, nobody here is my client, and none of this is legal advice--you want legal advice, hire a lawyer.
Now, to the meat of the questions, I don't know about the first one at all, and the second isn't very clear--what "splash screen" is being referred to, for example? If you mean the text console config utility, it's a perl script at /sbin/e-smith/console. For the web manager, /etc/e-smith/web/panels/manager looks like a good place to start.