Revoking The Evil Decree

The gemara in Rosh Hashana says that a decree against an individual can only be revoked during the aseres yemei tshuva [as the daf yomi learners know]. How then do we understand the gemara in Brachos where Yeshayahu told Chizkiyahu that he is going to die and Chizkiyahu answered that he has a tradition that no matter what, an evil decree can be revoked. Doesn't he know the gemara in Rosh Hashana that this only applies to a decree against the tzibbur but a decree against an individual cannot be revoked unless it is during the aseres yemei tshuva? [It is not likely to explain the gemara in Brachos as having transpired during the aseres yemei tshuva as the implication is that one can ALWAYS change an evil decree. The Turei Even offers an answer but it is contradicted by a few gemaras....]