Internet Sharing is not covered under the S.E plan just like either are the Sprint Tv premium channels. Tethering is not free in anyway its P.A.M (Phone as Modem $39.99 a month) on your bill if you pay for it.
If you do the reg edit it will work and you should slide under the radar and not get charged I have never had a issue with sprint over this.
Ya might want to be careful until you get your first bill just to be on the safe side, but again I have used it for over a year with no issues.
I have the S.E plan with no P.A.M. Another thread about it with some info
HERE.