Hi Neil,
I dont know which board do You use, I use M52233DEMO. There is MAC adress 00-00..-00 from begining (the same in the simulator). If You change it, its stored in memory flash, so when You erase it, You can change it again. You can read uTasker tutorial for M5223xto see how to change MAC adress. If You use demo Web pages (supplied with uTasker project) You can change there MAC adress and IP Adress as You want (Ok, You can change MAC adress just once, till You reflash the board). Now, You dont need develop any utilities for change it, because You can use (or modify) demo as its suplied.
I have to say the system in the demo is quite sophisticated, because You have to verify all changed parameters in 3 mins. after change is made. If You dont do it (according to inaccesibility of the network, or so), board will change setting back in the last working configuration and You can use old setting as before. I think that its a quite lot of work make Your own solution, so why dont use good proven solution? Of course, You can change everything because You have all source files (and web page sources too), but I will basicaly use this solution too.
For Me, the uTasker is quite large project and I dont familliar with it yet, But I really like it and enjoy to learn it. I have to say Mark made looot of work with it (and really support it), so when I will be able to work with uTasker better, I will use it in any project with ethernet I make. Reason is due to support, features and size of code. And The price for it is sooo low...
Regards, Rad