Proposition 10 changes the length of an unexpired term caused by the automatic resignation of an elected official due to the official declaring his or her candidacy for another office.  Under current law, the automatic resignation would be for an official who has one year left on his or her term.  This amendment pushes the length to one year and 30 days in order to save costs for a special election.

You can find more information here: http://www.lrl.state.tx.us/legis/billsearch/text.cfm?legSession=82-0&billtypeDetail=SJR&billNumberDetail=37&billSuffix=&startRow=1&IDlist=&unClicklist=&number=100