My sister is executor of my mother's estate;she and the attorney want me to sign a waiver of notice of probate?

Probably not.

Generally, most states require that all heirs or potential heirs either be sent formal notice (often requiring it to be served by sheriff, etc), or waive notice. By waiving notice, you aren't turning down your right to inspect the proceedings, and generally you will get a copy of any pleadings anyway. This simplifies things for the estate administration and reduces to cost to the estate.

If you have a reason not to trust your sister, then consult a probate attorney licensed in that jurisdiction on the specific steps you can take. For a referral, contact the local or state bar association.

A properly drawn will should have a clause revoking any previous one. If that's so, any previous will is completely worthless. The executor can't change the terms of a will, he/she is required to abide by it. The executor or administrator are watched over by the court to make sure their actions abide by the law. For instance, they would have to gain permission of the court to sell property owned by the estate. These representatives are paid actual expenses incurred in managing and settling the estate. In addition, the normal fee paid is around 2% of the value of the estate. If the estate is large, this 2% fee is usually reduced. These payments to the representative are governed by the manner in which the person performs their duties in settling the estate. If they do not perform satisfactorily, the court can order a reduction in the pay they receive. This fee income is subject to income tax. If you're concerned about something devious being done with a will, I'd strongly suggest you consult a solicitor for guidance. As beneficiaries you don't have much input into the process, but we all have a duty to see that the law is observed.

You need to hire an attorney to advise you about your rights but signing the waiver will not affect what you will ultimately receive. Further, refusing to sign may make the estate take longer to settle, which could possibly result in higher legal fees.

I would have a qualified person look at this first. It could be to your advantage. As it saves court cost. Leaves more in the estate. But the fine print. Best know all the details.