Okay all steps I do are :

1. root (busybox 1.6.1 build in shell ash...)
2. ifconfig wlan0 down
3. macchanger --r(andom) wlan0
4. ifconfig wlan0 up

If I don't do step 2 and 4 macchanger says :
"ERROR: Can't change MAC : interface up or not permission : Device or resource busy"
So to use the full trial I should not generate a random MAC but set every time I start the app the MAC with which I activated the 7 day trial right?

But I don't know why WPA does not allow reconnecting with another mac although the password is right while connecting ^^
It seems to recognize the MAC-ID fake right?

Edit :
I found out I don't need step 2 and 4 if I disconnect before changing.
Btw I think you wonder about the macchanger. It is an app from the repositorys i have