RenameVar(matFName, originalVarName, newVarName)

This function replaces the name of a variable ('originalVarName') in a mat file ('matFName') with a new variable name ('newVarName').
Usage: RenameVar(matFName, originalVarName, newVarName)

Example:
a=1; b=2; c=3; save('A','a','b','c');
whos('-file','A')
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Name Size Bytes Class Attributes
a 1x1 8 double
b 1x1 8 double
c 1x1 8 double
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RenameVar('A','a','a1');
whos('-file','A')
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Name Size Bytes Class Attributes
a1 1x1 8 double
b 1x1 8 double
c 1x1 8 double
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