@DM's answer is correct, but maybe not as straightforward as the OP might prefer.
Usually a disclaimer is made by giving timely written notice in proper form to the person who is in control of the inherited asset (using the word "inherited" in a broad non-technical sense) within the time allowed by statute. But, this can only be done if the rule that is stated in Utah Probate Code Section 75-2-801(5) does not prevent the person from doing that. This rule can be paraphrased as follows:
You cannot disclaim once you have taken actions consistent with ownership or you have waived the right to disclaim in writing.
An example may be helpful.
The classic screw up that gets made is that a surviving spouse is the beneficiary of a large life insurance policy (for example, $30,000,000). If the surviving spouse (who may have only a few years to live herself) receives these life insurance benefits, they will be subject to estate taxation at her death if not spent by then, and then will be subject to estate tax again when she leaves it to her children and they die owning those funds. But, if the wife had predeceased her husband, the funds would have gone to the children without being subject to estate taxation in the predeceased wife's estate. The tax at the death of the surviving spouse (who also had other substantial assets of her own) would be $10,000,000.
So, the family combined will pay significantly more taxes if the widow receives the benefits rather than they will if she disclaims the life insurance policy benefits, in which case they go to the secondary beneficiaries of the policy (the decedent and the surviving spouse's children in the next generation) without facing estate taxation in the named beneficiary surviving spouse's generation.
But, an overeager life insurance agent, trying to be helpful, gives the beneficiary a checkbook which allows the beneficiary to write checks against the amount due on the policy pending a full payout, and the surviving spouse uses the checkbook to pay a $10,000 funeral bill before conferring with a lawyer or accountant.
By doing so, the surviving spouse has lost the right to disclaim any of the $30,000,000 of funds payable from the life insurance policy pursuant to Utah Probate Code Section 75-2-801(5)(c). So, the overeager life insurance agent's attempt to bill helpful results in many millions of dollars of unnecessary tax liability for the family of the decedent.
The theory behind this harsh rule is to prevent people from "having it both ways." You either inherit something or you decline to accept the inheritance. Once you have taken any action that reveals an intent to do on or the other of these things, you aren't allowed to change your mind.
