If you don't need all the strings in their 'manipulated' form at the exact same time you could always manually copy from FLASH to RAM buffer and do the manipulation there. The buffer can be used for any number of string manipulations.There is no way to add more RAM so whatever you connect to store strings you will have to copy the string into RAM to manipulate it and copy it back out to auxiliary memory for free up the RAM for the next manipulation. There is a type of SPI memory called FRAM that I have heard is both non-volatile and fast: http://www.kerrywong.com/2012/01/15/using-fram-as-nonvolatile-memory-with-arduino/
512 bytes of non-volatile, ultra-lower power memory via I2C, which directly replaces EEPROM and FLASH.
Quote from: Pierre7 on Mar 28, 2014, 12:27 pm512 bytes of non-volatile, ultra-lower power memory via I2C, which directly replaces EEPROM and FLASH.They mean that the FRAM chip has the same interface as common EEPROM and FLASH chips so it can be used as a drop-in replacement for such chips.