Here is a script you can run on the ESXi host to add an annotation into multiple vmx files:
SAVEIFS=$IFS
IFS=$(echo -en "\\n\\b")
for i in \`find /vmfs/volumes/ -name \*.vmx\`
do
echo Filename:$i
echo Backing up VMX...
cp $i $i.bak
echo Backup complete...
echo adding the annotation:
echo "annotation = \\"<Fill the annotation text here without the angle braces>\\"" >> $i
echo Update done...
read -p "Hit any key to continue..."
done
IFS=$SAVEIFS