A method and data processing apparatus for remapping selected data access requests issued by a processor for accessing data items stored on a ROM. The method comprises the following steps: storing at least one replacement data item corresponding to at least one data item and different to said at least one data item in a portion of a RAM memory block, said RAM memory block being accessible by said processor, and said portion having been defined for storage of said at least one replacement data item; intercepting a data access request from said processor to said ROM; comparing at least a portion of an address of said intercepted data access request with a stored at least one identifier, said stored at least one identifier identifying an address of at least one data item stored on said ROM, and depending on said comparison either: remapping said data access request to said RAM memory block, such that a replacement data item stored on said memory block is accessed if said comparison indicates said at least a portion of an address to correspond to an address identified by said at least one identifier; or if said comparison indicates said at least a portion of an address not to be an address identified by said at least one stored identifier accessing a data item located at a position corresponding to said address on said ROM.