To change the data source name, you need to check its current value and then issue single rrdtool command.

Check the data source (DS) name.

$ rrdtool info graph_memory.rrd  | grep ^ds | sed 's/.*\[\(.*\)\].*/\1/g' | uniq
memFree
$ rrdtool dump graph_memory.rrd | grep name
  <name>memFree</name>

Change data source name from memFree to memoryFree.

$ rrdtool tune graph_memory.rrd -r memFree:memoryFree
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