Wills can be amended or revoked at any time during the individual's lifetime, offering flexibility for changing circumstances. In the case of revocable trusts, the grantor can also make changes or revoke the trust if necessary. However, irrevocable trusts cannot be altered or revoked by the grantor once established. It's essential to understand the specific features and limitations of your chosen estate planning instrument and consult with professionals when considering changes to your will or trust.