By default RivaTuner parses VGA BIOS clock initialization scripts to change clock frequencies on ATI RADEON X1000 display adapters. 
Unlike ATI's own script parsers executing the scripts completely, RivaTuner's VGA BIOS parser is intelligent and can programmatically skip some portions of scripts causing undesired side effects like automatic memory timings tuning performed when memory clock frequency is changed via ATI OverclockerX1K or CCC. 
RivaTuner gives you both methods and allows you either to change memory clock frequency only or to allow the parser to autotune timings syncronically with memory clock frequency change. 
You may set this entry to 1 to allow the parser to autotune the timings.