Hello Juan,
If you want disalbe the NMI interrupt, please use the Flash Option Register (FTFA_FOPT) ->
NMI_DIS bit :

On the KSDk project code ,, only need change here :

to
.long 0xFFFFFFFF
.long 0xFFFFFFFF
.long 0xFFFFFFFF
.long 0xFFFFFBFE
Hope it helps
Alice